Late Holocene stormtrajectory changes inferred from the oxygen isotope composition of lake diatoms, south Alaska

Analyses?18O of carbonate minerals were conducted on a Finnigan-MAT 252 isotope ratio mass spectrometer with a Kiel II automated carbonate preparation device;

DK: Chronlogy based on existing published version, but has been updated in 2018, but not yet publised. Upate affects ages older than 11 ka.

Homogenized 1 cm subsamples were pretreated for isotope analysis by 24 h digestion in ~45 ml of 2.5% sodium hypochlorite, then sieved (125 ?m) to remove ostracode shells and other coarse materials

Oxygen isotopes point toward maximum evaporative forcing early in the Holocene, by or before 9000 cal. yr BP. Mineralogical indicators of lake salinity decline gradually after 6000 cal. yr BP but freshening was episodically reversed and modern lake geochemistry was achieved late in the Holocene, after 1400 cal. yr BP. The Lateglacial?Holocene transition is marked by an abrupt and sustained geochemical anomaly reflecting reduced evaporative forcing and lake freshening...Oxygen isotopes record a rich spectrum of high-frequency variation interpreted as dominantly transient response to fluid balance change, but are relatively insensitive to low-frequency changes better reflected in sediment mineralogy. Oxygen and carbon isotopes covary closely at high frequencies but are decoupled at low frequencies by longterm lake basin changes in carbon cycling.

The persistent dominance of endogenic carbonate minerals requires a dynamic balance between groundwater inflow, evaporative concentration and groundwater outflow. "Fluid balance"In groundwater-dominated lakes, sediment geochemistry becomes closely linked to changes in lake?groundwater exchange and groundwater recharge at all timescales.

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