<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:p>The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.</jats:p>
<jats:p>The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.</jats:p>
<jats:p>The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.</jats:p>
<jats:p>The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.</jats:p>
<jats:p>The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.</jats:p>
<jats:p>The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.</jats:p>
<jats:p>The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.</jats:p>
<jats:p>The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the same pattern across terminations, implying that the processes that initiated climate change in the Southern Ocean has varied through time.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>We use a Generalized Additive Model (GAM) to provide the first winter sea ice concentration record from two cores located within the southwest Pacific sector of the Southern Ocean. To compliment the application of GAM, a time series analysis on satellite records of sea ice concentration data was used to extend the standard 13.25 year time series used for paleoceanography. After comparing GAM sea ice estimates with previously published paleo sea ice data we then focus on a new paleo winter sea ice record for marine sediment core E27‐23 (59°37.1'S, 155°14.3'E), allowing us to provide a more comprehensive view of winter sea ice dynamics for the southwest Pacific Ocean. The paleo winter sea ice concentration estimates provide the first suggestion that winter sea ice within the southwestern Pacific might have expanded during the Antarctic Cold Reversal. Throughout the Holocene, core E27‐23 documents millennial scale variability in paleo winter sea ice coverage within the southwest Pacific. Holocene winter sea ice expansion may have resulted from the Laurentide Ice Sheet deglaciation, increased intensity of the westerly winds, as well as a northern migration of the Subtropical and/or Sub‐Antarctic Fronts. Brief consideration is given to the development of a paleo summer sea ice proxy. We conclude that there is no evidence that summer sea ice ever existed at core sites SO136‐111 and E27‐23 over the last 220 and 52,000 years, respectively.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>
<jats:title>Abstract</jats:title><jats:p>In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom‐bound N isotope (δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub>) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal‐ and barium‐based proxies for reduced export production during ice ages, the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> increases point to ice age reductions in the supply of deep ocean‐sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> changes are not the result of changing species composition. The pennate and centric assemblage δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality‐based interpretation of the centric‐to‐pennate δ<jats:sup>15</jats:sup>N<jats:sub>db</jats:sub> difference suggests that late summer surface waters became nitrate free during the peak glacials.</jats:p>