Description: As part of the return flow of the Atlantic overturning circulation, Antarctic Intermediate Water (AAIW) redistributes heat, salt, CO2 and nutrients from the Southern Ocean to the tropical Atlantic and thus plays a key role in ocean-atmosphere exchange. It feeds (sub) tropical upwelling linking high and low latitude ocean biogeochemistry but the dynamics of AAIW during the last deglaciation remain poorly constrained. We present new multi-decadal benthic foraminiferal Cd/Ca and stable carbon isotope (d13C) records from tropical W-Atlantic sediment cores indicating abrupt deglacial nutrient enrichment of AAIW as a consequence of enhanced deglacial Southern Ocean upwelling intensity. This is the first clear evidence from the intermediate depth tropical W-Atlantic that the deglacial reconnection of shallow and deep Atlantic overturning cells effectively altered the AAIW nutrient budget and its geochemical signature. The rapid nutrient injection via AAIW likely fed temporary low latitude productivity, thereby dampening the deglacial rise of atmospheric CO2.

Description: The water masses passing the Fram Strait are mainly responsible for the exchange of heat and freshwater between the Nordic Seas and the Arctic Ocean (the Arctic Mediterranean, AM). Disentangling their exact sources, distribution and mixing, however, is complex. This work provides new insights based on a detailed geochemical tracer inventory including dissolved Nd isotope (e-Nd), rare earth element (REE) and stable oxygen isotope (d18O) data along a full water depth section across Fram Strait. We find that Nd isotope and REE distributions in the open AM primarily reflect lateral advection of water masses and their mixing. Seawater-particle interactions exert important control only above the shelf regions, as observed above the NE Greenland Shelf. Advection of northward flowing warm Atlantic Water (AW) is clearly reflected by an e-Nd signature of -11.7 and a Nd concentration ([Nd]) of 16 pmol/kg in the upper ~500 m of the eastern and central Fram Strait. Freshening and cooling of the AW on its way trough the AM are accompanied by a continuous change towards more radiogenic e-Nd signatures (e.g. -10.4 of dense Arctic Atlantic Water). This mainly reflects mixing with intermediate waters but also admixture of dense Kara Sea waters and Pacific-derived waters. The more radiogenic e-Nd signatures of the intermediate and deep waters (reaching -9.5) are mainly acquired in the SW Nordic Seas through exchange with basaltic formations of Iceland and CE Greenland. Inputs of Nd from Svalbard are not observed and surface waters and Nd on the Svalbard shelf originate from the Barents Sea. Shallow southward flowing Arctic-derived waters (〈200 m) form the core of the East Greenland Current above the Greenland slope and can be traced by their relatively radiogenic e-Nd (reaching -8.8) and elevated [Nd] (21-29 pmol/kg). These properties are used together with d18O and standard hydrographic tracers to define the proportions of Pacific-derived (〈~30% based on Nd isotopes) and Atlantic-derived waters, as well as of river waters (〈~8%). Shallow waters (〈150 m) on the NE Greenland Shelf share some characteristics of Arctic-derived waters, but exhibit less radiogenic epsilon-Nd values (reaching -12.4) and higher [Nd] (up to 38 pmol/kg) in the upper ~100 m. This suggests local addition of Greenland freshwater of up to ~6%. In addition to these observations, this study shows that the pronounced gradients in epsilon-Nd signatures and REE characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the AM.

Description: New records of stable silicon isotope signatures (?30Si) together with concentrations of biogenic opal and organic carbon from the central (9°S) and northern (5°S) Peruvian margin reveal changes in diatom productivity and nutrient utilization during the past 20,000 years. The findings are based on a new approach using the difference between the ?30Si signatures of small (11-32 ?m) and large (〉150 ?m) diatom fractions (?30Si ) in combination with the variance in diatom assemblages for reconstruction Coscino-bSi of past upwelling intensity. Combination of our records with two previously published records from the southern upwelling area off Peru (12-15°S) shows a general decoupling of the environmental conditions at the central and southern shelf mainly caused by a northward shift of the main upwelling cell from its modern position (12-15°S) toward 9°S during Termination 1. At this time only moderate upwelling intensity and productivity levels prevailed between 9°S and 12°S interpreted by a more northerly position of Southern Westerly Winds and the South Pacific Subtropical High. Furthermore, a marked decrease in productivity at 12-15°S during Heinrich Stadial 1 coincided with enhanced biogenic opal production in the Eastern Equatorial Pacific, which was induced by a southward shift of the Intertropical Convergence Zone and enhanced northeasterly trade winds. Modern conditions were only established at the onset of the Holocene. Past changes in preformed ?30Si signatures of subsurface waters reaching the Peruvian Upwelling System did not significantly affect the preserved ?30Si signatures