basis: We conclude that, together with variations in seawater d18O, the pH effect on d18O of carbonates can obscure the temperature signal in the sponge d18O record sufficiently to explain the divergent trends of the Sr/Ca and the oxygen isotope records. These results indicate that for temperature reconstructions using C. nicholsoni skeletons, Sr/Ca is a more robust proxy than d18O.

direction: decrease

interpDirection: decrease

scope: climate

seasonality: Aug-Jul

variable: temperature

variableDetail: 20 mbsl

variableGroup: temperature and salinity

scope: climate

scope: climate

basis: The d18Owater salinity relation in the Caribbean is on the order of 0.2 to 0.3%/psu [Ruhlemann et al., 1999; Watanabe et al., 2001]. Oxygen isotope records of these sponges do notreveal reproducible temperature signals. Variations in thed18O of the ambient water and the pH effect on the oxygenisotopic composition of carbonates [Zeebe, 1999] mayobscure temperature signals in thed18O records.

coefficient: NA

direction: positive

equilibriumEvidence: The observation that sponges precipitate aragonite in chemical and isotopic equilibrium indicates that the composition of the precipitating fluid is hardly influenced by the sponge metabolism. Thus pH changes in the ambient seawater may be directly monitored by the d18O record of the sponge aragonite. This hypothesis is supported by the boron isotopic composition of sponge skeletons, which indicates mineralization under seawater pH conditions [Bo�hm et al., 2000b].

fraction: NA

inferredMaterial: seawater

integrationTime: 2to6

integrationTimeBasis: For U-Th analysis, 0.3 to 1g of sponge material was drilled along visible growth layers. The sample size was chosen so that the width and depth of the sampling groove was equivalent to a period of about 20 years, given a growth rate on the order of 0.2 mm/a. 11 samples were anayzed for U-Th. The external reproducibility of the U/Th dating results was determined as about �20 years (2sem) by five replicate analyses of sample Ce96-40 and confirmed by analysis of three closely spaced sample pairs (Ce96-45/51, Ce96-170/172, Ce96-123/40). For one sample pair (Ce96-184/186) U/Th ages could not be confirmed within external reproducibility. As the age data of this specimen deviate significantly from a linear growth curve, we fitted a third order polynomial to the U/Th ages.

integrationTimeUncertainty: 1-92 years

integrationTimeUncertaintyType: U-Th dating uncertainty

integrationTimeUnits: year

mathematicalRelation: linear

rank: 1

scope: isotope

variable: seawaterIsotope

variableGroup: EffectiveMoisture

variableGroupDirection: negative

variableGroupOriginal: d18O_seawater

basis: Temperature equation of Bohm et al. [2000]. Oxygen isotope records of these sponges do notreveal reproducible temperature signals. Variations in thed18O of the ambient water and the pH effect on the oxygenisotopic composition of carbonates [Zeebe, 1999] mayobscure temperature signals in thed18O records.

coefficient: NA

direction: negative

equilibriumEvidence: The observation that sponges precipitate aragonite in chemical and isotopic equilibrium indicates that the composition of the precipitating fluid is hardly influenced by the sponge metabolism. Thus pH changes in the ambient seawater may be directly monitored by the d18O record of the sponge aragonite. This hypothesis is supported by the boron isotopic composition of sponge skeletons, which indicates mineralization under seawater pH conditions [Bo�hm et al., 2000b].

fraction: NA

inferredMaterial: seawater

integrationTime: 6-Feb

integrationTimeBasis: For U-Th analysis, 0.3 to 1g of sponge material was drilled along visible growth layers. The sample size was chosen so that the width and depth of the sampling groove was equivalent to a period of about 20 years, given a growth rate on the order of 0.2 mm/a. 11 samples were anayzed for U-Th. The external reproducibility of the U/Th dating results was determined as about �20 years (2sem) by five replicate analyses of sample Ce96-40 and confirmed by analysis of three closely spaced sample pairs (Ce96-45/51, Ce96-170/172, Ce96-123/40). For one sample pair (Ce96-184/186) U/Th ages could not be confirmed within external reproducibility. As the age data of this specimen deviate significantly from a linear growth curve, we fitted a third order polynomial to the U/Th ages.

integrationTimeUncertainty: 1-92 years

integrationTimeUncertaintyType: U-Th dating uncertainty

integrationTimeUnits: year

mathematicalRelation: linear

rank: 2

scope: isotope

variable: temperature

variableGroup: Temperature

variableGroupDirection: negative

variableGroupOriginal: T_water

coefficient: NA

fraction: NA

rank: NA

scope: isotope

basis: d18O calibration to T assuming constant d18Ow

direction: decrease

interpDirection: decrease

scope: climate

seasonality: Aug-Jul

variable: temperature

variableDetail: 125 mbsl

variableGroup: temperature and salinity

scope: climate

scope: climate

basis: The d18Owater salinity relation in the Caribbean is on the order of 0.2 to 0.3%/psu [Ruhlemann et al., 1999; Watanabe et al., 2001]. Oxygen isotope records of these sponges do notreveal reproducible temperature signals. Variations in thed18O of the ambient water and the pH effect on the oxygenisotopic composition of carbonates [Zeebe, 1999] mayobscure temperature signals in thed18O records.

coefficient: NA

direction: positive

equilibriumEvidence: The observation that sponges precipitate aragonite in chemical and isotopic equilibrium indicates that the composition of the precipitating fluid is hardly influenced by the sponge metabolism. Thus pH changes in the ambient seawater may be directly monitored by the d18O record of the sponge aragonite. This hypothesis is supported by the boron isotopic composition of sponge skeletons, which indicates mineralization under seawater pH conditions [Bo�hm et al., 2000b].

fraction: NA

inferredMaterial: seawater

integrationTime: 2to6

integrationTimeBasis: For U-Th analysis, 0.3 to 1g of sponge material was drilled along visible growth layers. The sample size was chosen so that the width and depth of the sampling groove was equivalent to a period of about 20 years, given a growth rate on the order of 0.2 mm/a. 4 samples were anayzed for U-Th. 10 samples for radiocarbon analysis were removed. They compared D14C data with a D14C curve measured on a Florida surface water coral [Druffel, 1989]. The fit was constrained by assuming that the growth rate was constant in the relevant part of the sponge skeleton. They further assume that the timing of the radiocarbon increase at 125 mbsl was similar to surface waters in that region because the amplitude of change in D14C is similar to the surface water change. For specimen Pb19 a mean growth rate of 0.19 mm/a was calculated from the slope of a linear fit to the dated tie points. A lifespan from about 1400 A.D. to 1996 A.D. was determined by extrapolating the mean growth rate to the base of the skeleton. The U/Th chronology is independently confirmed by the correct localization of the nuclear weapon test radiocarbon increase at a depth of about 5.9 mm below the surface of the skeleton (Figure 6, Table 2). Further independent support for the reliability of our chronologies is provided from the fit of d13C data of the investigated sponge skeletons and atmospheric CO2 records [Bo�hm et al., 2002].

integrationTimeUncertainty: 1-25 years

integrationTimeUncertaintyType: U-Th dating uncertainty

integrationTimeUnits: year

mathematicalRelation: linear

rank: 1

scope: isotope

variable: seawaterIsotope

variableGroup: EffectiveMoisture

variableGroupDirection: negative

variableGroupOriginal: d18O_seawater

basis: Temperature equation of Bohm et al. [2000]. Oxygen isotope records of these sponges do notreveal reproducible temperature signals. Variations in thed18O of the ambient water and the pH effect on the oxygenisotopic composition of carbonates [Zeebe, 1999] mayobscure temperature signals in thed18O records.

coefficient: NA

direction: negative

equilibriumEvidence: The observation that sponges precipitate aragonite in chemical and isotopic equilibrium indicates that the composition of the precipitating fluid is hardly influenced by the sponge metabolism. Thus pH changes in the ambient seawater may be directly monitored by the d18O record of the sponge aragonite. This hypothesis is supported by the boron isotopic composition of sponge skeletons, which indicates mineralization under seawater pH conditions [Bo�hm et al., 2000b].

fraction: NA

inferredMaterial: seawater

integrationTime: 6-Feb

integrationTimeBasis: For U-Th analysis, 0.3 to 1g of sponge material was drilled along visible growth layers. The sample size was chosen so that the width and depth of the sampling groove was equivalent to a period of about 20 years, given a growth rate on the order of 0.2 mm/a. 4 samples were anayzed for U-Th. 10 samples for radiocarbon analysis were removed. They compared D14C data with a D14C curve measured on a Florida surface water coral [Druffel, 1989]. The fit was constrained by assuming that the growth rate was constant in the relevant part of the sponge skeleton. They further assume that the timing of the radiocarbon increase at 125 mbsl was similar to surface waters in that region because the amplitude of change in D14C is similar to the surface water change. For specimen Pb19 a mean growth rate of 0.19 mm/a was calculated from the slope of a linear fit to the dated tie points. A lifespan from about 1400 A.D. to 1996 A.D. was determined by extrapolating the mean growth rate to the base of the skeleton. The U/Th chronology is independently confirmed by the correct localization of the nuclear weapon test radiocarbon increase at a depth of about 5.9 mm below the surface of the skeleton (Figure 6, Table 2). Further independent support for the reliability of our chronologies is provided from the fit of d13C data of the investigated sponge skeletons and atmospheric CO2 records [Bo�hm et al., 2002].

integrationTimeUncertainty: 1-25 years

integrationTimeUncertaintyType: U-Th dating uncertainty

integrationTimeUnits: year

mathematicalRelation: linear

rank: 2

scope: isotope

variable: temperature

variableGroup: Temperature

variableGroupDirection: negative

variableGroupOriginal: T_water

coefficient: NA

fraction: NA

rank: NA

scope: isotope

basis: lower limit of 95% ci of difference in Sr/Ca between -20 and -125m, divided by difference in observed T at those depths.

direction: decrease

interpDirection: decrease

scope: climate

seasonality: Aug-Jul

variable: temperature

variableDetail: sea@surface

variableDetailOriginal: sea_surface

variableGroup: Temperature

variableGroupDirection: negative

variableGroupOriginal: T

variableOriginal: temperature

scope: climate

scope: climate

coefficient: NA

fraction: NA

inferredMaterial: seawater

rank: NA

scope: isotope

coefficient: NA

fraction: NA

rank: NA

scope: isotope

coefficient: NA

fraction: NA

rank: NA

scope: isotope

basis: lower limit of 95% ci of difference in Sr/Ca between -20 and -125m, divided by difference in observed T at those depths.

direction: decrease

interpDirection: decrease

scope: climate

seasonality: Aug-Jul

variable: temperature

variableDetail: sea@surface

variableDetailOriginal: sea_surface

variableGroup: Temperature

variableGroupDirection: negative

variableGroupOriginal: T

variableOriginal: temperature

scope: climate

scope: climate

coefficient: NA

fraction: NA

inferredMaterial: seawater

rank: NA

scope: isotope

coefficient: NA

fraction: NA

rank: NA

scope: isotope

coefficient: NA

fraction: NA

rank: NA

scope: isotope