ALBERT

Description: The Leeuwin Current flowing southward along West Australia is an important conduit for the poleward heat transport and interocean water exchange between the tropical and the subantarctic ocean areas. Its past development, and its relationship to Southern Ocean change and to Australian ecosystem response, however is largely unknown. We here reconstruct sea surface and thermocline temperatures and salinities from foraminiferal-based Mg/Ca and stable oxygen isotopes from offshore southwest and southeast Australia reflecting the Leeuwin Current dynamics over the last 60 kyrs. Its variability resembles the biomass burning development in Australasia from ~60–20 ka BP implying that climate-modulated changes related to the Leeuwin Current most likely affected Australian vegetational and fire regimes. In particular during ~60–43 ka BP, warmest thermocline temperatures point to a strongly developed Leeuwin Current during Antarctic cool periods when the Antarctic Circumpolar Current weakened. The pronounced centennial-scale variations in Leeuwin Current strength appear in line with the migrations of the Southern Hemisphere frontal system and are captured by prominent changes in the Australian megafauna biomass. We argue that the concerted action of a rapidly changing Leeuwin Current, the ecosystem response in Australia, and human interference since ~50 BP enhanced the ecological stress on the Australian megafauna until a tipping point was reached at ~43 ka BP, after which faunal recuperation no longer took place. While being weakest during the last glacial maximum, the deglacial Leeuwin Current intensified at times of poleward migrations of the Subtropical Front. During the Holocene, the thermocline off South Australia was considerably shallower compared to the short-term glacial and deglacial periods of Leeuwin Current intensification.

Description: During the last deglaciation abrupt millennial‐scale perturbations of the Atlantic Meridional Overturning Circulation massively altered the interhemispheric heat distribution affecting, for example, continental ice volume and hydroclimate. If and how the related cross‐equatorial heat transport was controlled by the interplay between the southward‐flowing Brazil Current (BC) and northward‐flowing North Brazil Current (NBC) remains controversial. To assess the role of tropical heat transport during the last deglaciation, we obtained a high‐resolution foraminiferal Mg/Ca‐based sea surface temperature (SST) record from the BC domain at 21.5°S. The data reveal a yet undocumented warming of at least 4.6°C of the BC during Heinrich Stadial 1 at ∼16 ka indicating massive oceanic heat accumulation in the tropical South Atlantic. Simultaneously, a strongly diminished NBC prevented the release of this excess heat into the northern tropics. The observed magnitude of heat accumulation substantially exceeds numerical model simulations, stressing the need to further scrutinize atmospheric and oceanic heat transport during extreme climatic events.

Description: Stable carbon (δ13C) and oxygen isotope (δ18O) were performed on the benthic foraminiferal species Uvigerina spp. The foraminiferal specimens were selected from piston core M78/1-235-1, which was recovered from Tobago Basin (11°36.53'N 60°57.86'W) from 852 m water depth during R/V Meteor Cruise 78/1. Sampling and analytical studies were carried out from 412.5 to 800 cm core depth at 2-4 cm spatial resolution. This dataset extends the existing benthic proxy records (Poggemann et al., 2017; doi:10.1029/2018PA003376) further back in time, now focusing on the glacial time period and the latest fully developed D/O events (~22.7-37 ka BP). The isotope analyses were performed in 2017 and 2019 on a Thermo Scientific MAT 253 mass spectrometer with an automated Kiel IV Carbonate Preparation Device. The proxy data provide stratigraphical information on the Tobago Basin core M78/1-235-1.

Description: Stable carbon (δ13C) and oxygen isotope (δ18O) and Mg/Ca-measurements were performed on the planktonic subsurface-dwelling foraminiferal species Globorotalia truncatulinoides. The foraminiferal specimens were selected from piston core M78/1-235-1, which was recovered from Tobago Basin (11°36.53'N 60°57.86'W) from 852 m water depth during R/V Meteor Cruise 78/1. Sampling and analytical studies were carried out from 630 to 800 cm core depth at 1-2 cm spatial resolution. This dataset extends the existing subsurface proxy records (Reißig et al., 2019; doi:10.1594/PANGAEA.897083) further back in time, now focusing on the time period of the latest fully developed D/O events (~30-37 ka BP). The isotope analyses were performed in 2019 on a Thermo Scientific MAT 253 mass spectrometer with an automated Kiel IV Carbonate Preparation Device. Trace metal analyses were performed on a VARIAN 720-ES Axial ICP-OES, a simultaneous, axial-viewing Inductively Coupled Plasma - Optical Emission Spectrometer coupled to a VARIAN SPS3 sample preparation system. The proxy data provide information on the Tobago Basin subsurface hydrography in relation to Western Boundary Current and North Atlantic Subtropical Gyre interdynamics.

Description: This dataset provides depth, age, and sediment reflectance data of piston core M78/1-235-1, which was recovered from Tobago Basin (11°36.53'N 60°57.86'W) from 852 m water depth. A MINOLTA CM-508d hand-held spectrophotometer was used during R/V Meteor Cruise 78/1 to measure the light reflectance (L*) of the sediment. The spectral reflectance is measured over a wavelength spectrum from 400 to 700 nm at a 10 nm pitch. Routine measurements were made at 1 cm intervals and automatically recorded using the SPECTRAMAGIC® v.2.11 software. The L*- dataset without age information is archived at doi:10.1594/PANGAEA.788740 (Bahr et al., 2012). The L* data provide stratigraphical information, and information on fluvial supply of terrigenous matter to the core location.

Description: We generated alkenone- and TEX86- based paleotemperature estimates for MIS 6-5 in core M125-55-7 (offshore Eastern Brazil) to text whether previously generated foraminiferal Mg/Ca SST are seasonaly biased. We find that alkenone and Mg/Ca-temperatures reflect annual mean SST with a transient winter bias of alkenone SST during MIS 5a-c. The winter-bias might relate to increased upwelling activity as indicated by higher abundances of G. bulloides. TEX86 temperatures (despite showing annual mean SST in core tops) deviate by up to 6°C to lower temperatures which we attribute to increased input of terrestrial GDGT during MIS 6 as indicated by an high BIT index and (ii) migration of the TEX86 producers to deeper levels within the water column following changes in vertical particle flux efficiency.