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Abstract The delivery of nutrients from intermediate waters that form in the Southern Ocean is thought to be a key control on tropical ocean surface productivity. In this paper, we present geochemical evidence that an increase in low‐latitude productivity during the Last Interglacial (LIG) was driven by an increase in the preformed nutrient content of Subantarctic Mode Water (SAMW). We generated records of benthic foraminiferal δ¹³C, δ¹⁸O, Cd/Ca and Mg/Li which are used to reconstruct seawater cadmium, dissolved oxygen, and temperature from a core site in the Florida Straits. The Florida Straits is a location of mixing between SAMW and Northern Component Water, the ratio of which is dependent on the strength of the Atlantic Meridional Overturning Circulation. We find that Late LIG seawater cadmium—which in today's ocean is correlated to phosphate—was substantially higher than the Late Holocene (LH) average at this location, while apparent oxygen utilization was similar during these two periods. Thus, we invoke higher preformed phosphate in the Florida Straits during the Late LIG relative to the LH. Increased SAMW preformed phosphate could be the result of reduced Antarctic Zone winter mixed layer residence time and greater Southern Ocean surface nutrient supply during the Late LIG compared to the LH, as supported by published reconstructions of Southern Ocean biogeochemistry and dynamics. We therefore hypothesize that higher SAMW preformed phosphate would cause an increase in the transport of nutrients into the low latitudes, thereby increasing productivity there. 

Abstract Upwelling deep waters in the Southern Ocean release biologically sequestered carbon into the atmosphere, contributing to the relatively high atmospheric CO₂levels during interglacial climate periods. Paleoceanographic evidence suggests this “CO₂leak” was lessened during the last glacial maximum (LGM), potentially due to increased stratification, weaker and equatorward‐shifted winds, and/or enhanced biological carbon export. The collective influences of these mechanisms on the ocean's biological pump efficiency and amount of atmospheric CO₂can be quantified by determining preformed phosphate of deep waters. We quantify preformed PO₄(P_pre,AOU) and preformed() of LGM bottom waters using a compilation of published paleo‐temperature, nutrient and oxygen estimates from benthic foraminifera. Our results show that preformed phosphate of the Pacific and Indian deep oceans was reduced by about −0.53 ± 0.13 μM and suggest that much (64 ± 28 ppmv) of the Glacial‐Interglacial CO₂drawdown resulted from changes in the ocean's biological pump efficiency. Once carbonate compensation is accounted for, this can explain the entire CO₂drawdown (87 ± 40 ppmv). Preformedshows similar results. The reconstructed LGM P_pre,AOUand oxygen are qualitatively consistent with the changes produced by a suite of numerical sensitivity experiments that roughly simulate three proposed mechanisms for an increase in LGM biological pump efficiency: an increase in biological activity, a decrease in wind‐driven upwelling, and an increase in stratification in the Southern Ocean. 

Two collocal cores were recovered at approx. 542 meters depth in the Bahamas side of the Florida Straits. Benthic foraminifera species Planulina ariminensis and Hoeglundina elegans, as well as Globobulimina spp., were picked from the greater-than 250-micron size fraction. Mass spectrometry methods were used to analyze P. ariminensis and Globobulimina spp. tests for carbon and oxygen isotopic ratios while H. elegans tests were analyzed for the cadmium/calcium, magnesium/calcium, and lithium/calcium ratios. The records extend from the Late Holocene to the Penultimate Glacial Maximum (Marine Isotope Stage [MIS] 6), with high sedimentation rates during peak interglacial periods (MIS 1 and 5e). Elemental ratios were measured by reductively and oxidatively cleaning the samples following Boyle and Rosenthal (1996), and then using a Thermo Finnigan Element2 Magnetic Sector Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) at the Institute of Alpine and Arctic Research, University of Colorado, Boulder (INSTAAR) according to the methods of Marchitto (2006).Stable oxygen and carbon isotopic ratio data (δ18O and δ13C, respectively) for all samples of P. ariminensis and 51 out of 70 total samples of Globobulimina spp. were acquired using a Thermo MAT 253 with Kiel carbonate preparation device at the Georgia Institute of Technology (GT). 19 replicate samples of Globobulimina were analyzed at the University of Arizona with the same methods.The temperature reconstruction uses the Mg/Li-based calibration proposed by Marchitto et al. (2018)The oxygen content reconstruction uses the benthic foraminiferal epifaunal-infaunal δ13C gradient proxy, specifically the recently updated calibration described in Hoogakker et al. (2025). 

The high rate of biological productivity in the North Atlantic is stimulated by the advective supply of nutrients into the region via the Gulf Stream (nutrient stream). It has been proposed that the projected future decline in the Atlantic Meridional Overturning Circulation (AMOC) will cause a reduction in nutrient supply and resulting productivity. In this work, we examine how the nutrient stream changed over the Younger Dryas climate reversal that marked the transition out of the last ice age. Gulf Stream nutrient content decreased, and oxygen content increased at the Florida Straits during this time of weakened AMOC. The decreased nutrient stream was accompanied by a reduction in biological productivity at higher latitudes in the North Atlantic, which supports the link postulated in theoretical and modeling studies. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Paleoceanography. The data include parameters of paleoceanography with a geographic location of North Atlantic Ocean. The time period coverage is from 35000 to 0 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Climate Reconstruction. The data include parameters of paleoceanography with a geographic location of North Atlantic Ocean. The time period coverage is from 1930 to -52 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data.