ALBERT

Description: Supplementary material for Martínez Fontaine et al., 2019 (Table S1), including the radiocarbon ages in benthonic and planktonic foraminifera in six cores in the Chilean margin, beetween ~31°S and ~36°S (Table S3). The age models for the cores are detailed in Martínez Fontaine et al., 2019 and were produced using the information on planktonic δ13C (Table S2). Also included are the Δ14C resulting from the age models.

Description: Past glacial-interglacial increases in the concentration of atmospheric carbon dioxide (CO2) are thought to arise from the rapid release of CO2 sequestered in the deep sea, primarily via the Southern Ocean. Here, we present radiocarbon evidence from the Atlantic sector of the Southern Ocean that strongly supports this hypothesis. We show that during the last glacial period, deep water circulating around Antarctica was more than two times older than today relative to the atmosphere. During deglaciation, the dissipation of this old and presumably CO2-enriched deep water played an important role in the pulsed rise of atmospheric CO2 through its variable influence on the upwelling branch of the Antarctic overturning circulation.

Description: Sea surface temperature calculated from counts of the planktonic foraminifera N. pachyderma; planktonic and benthic foraminifera d18O and d13C for cores MD07-3076Q (covering the last deglaciation) and MD07-3077 (covering Termination V).

Description: In the Southern Ocean (SO), climate-driven latitudinal migrations of the Antarctic Circumpolar Current (ACC) frontal system impact large-scale ocean circulation and primary productivity. Latitudinal migrations may not have been identical in all SO basins due to the presence or absence of regional bathymetric obstacles. The Antarctic Polar Front (APF), defined by the 3–5 ◦C surface temperature range and the 2 ◦C subsurface temperature minimum at 200 m, is particularly important for nutrient redistribution and biodiversity, influencing the soft tissue carbon pump in the modern SO. However, previous assessments of its migrations in the past, mostly based on a single metric or indirect observations, were not always robust. Here, we combine a new proxy for subsurface temperature (sub-ST) reconstructions based on radiolarian assemblages (sub-STrad), with relative abundance variations of key radiolarian species, and sea-surface temperatures (SST) reconstructions, based on diatom assemblages (SSTdiat), to refine estimations of the past mean APF locations in the Kerguelen Plateau (KP) region. Data from three sediment cores on a south (55◦S) to north (47◦S) transect are used to trace the mean APF locations for three climate states, glacials, peak-interglacials and mild-interglacials. Our results suggest that the APF, presently located south of Kerguelen Islands, shifted by 6–7 degrees of latitude and was located north of the KP during all glacial periods of the last 360 kyrs. This suggests that the ACC major flow interacted less with the bottom topography relative to its modern counterpart, probably resulting in less mixing of the water column over and in the lee of the KP. We propose that this process participated in the isolation of Antarctic surface waters (AASW) and in the reduction of macro-nutrient supply, thus resulting in lower regional productivity. During the warmer-than-present early interglacial periods, the APF probably migrated south by ~5 degrees of latitude relative to its modern position, to pass through the Fawn Trough. Contrary to glacial periods, the APF was forced in an “S” shape while the ACC main flow was constrained against the northern tip of the KP. In this configuration, a stronger interaction between the ACC, its associated fronts, and topography is expected, resulting in more mixing of the water column over and east of the KP. Congruently, siliceous productivity was probably restrained to latitudes south of the Fawn Trough.

Description: The Southern Ocean plays a prominent role in the Earth's climate and carbon cycle. Changes in the Southern Ocean circulation may have regulated the release of CO2 to the atmosphere from a deep-ocean reservoir during the last deglaciation. However, the path and exact timing of this deglacial CO2 release are still under debate. Here we present measurements of deglacial surface reservoir 14C age changes in the eastern Pacific sector of the Southern Ocean, obtained by 14C dating of tephra deposited over the marine and terrestrial regions. These results, along with records of foraminifera benthic-planktic 14C age and d13C difference, provide evidence for three periods of enhanced upwelling in the Southern Ocean during the last deglaciation, supporting the hypothesis that Southern Ocean upwelling contributed to the deglacial rise in atmospheric CO2. These independently dated marine records suggest synchronous changes in the Southern Ocean circulation and Antarctic climate during the last deglaciation.

Description: The comparison between different climate model simulations of water hosing experiments under glacial conditions points toward diverging responses in Sea Surface Temperature changes (SST) especially in the Southeast Pacific (SEP). This suggests that reconstituting the latitudinal SST gradient in the SEP is a critical parameter for a better understanding of the mechanisms behind the abrupt climatic events since the last glacial period. Here we present, high-resolution records of SST, using planktonic foraminiferal assemblages and alkenone temperature reconstructions and stable oxygen and carbon isotopes from three deep-sea sediment cores along a latitudinal transect off the southern Chilean coast. This allowed us to reconstruct the variations of the latitudinal SST gradient and the Subtropical Front movements in the SEP. The SST results suggest a clear Antarctic timing consistent with the bipolar seesaw control, especially during the late glacial and the deglaciation. Our records do not suggest a complete oceanic heat transfer signal, highlighting the implication of an atmospheric component in the heat transfers between the two hemispheres, controlled by the latitudinal movements of the intertropical convergence zone in the Atlantic and the associated weaker South Pacific westerly split jet. Furthermore, our records indicate variable conditions during the Holocene, and also emphasize the influence of local fresh water inputs from the Patagonian ice sheet and/or precipitation on the SST fresh water input estimates along the Chilean margin (North and South of 49° S) from the onset of the deglaciation until 8 kyr cal. BP.

Description: Supplementary material for Martínez Fontaine et al., 2021: Post–glacial tephrochronology record off the Chilean continental margin (~41° S). Including: Table S1.- Globigerina bulloides δ18O and the resulting age model for core MD07-3098 with its respective 1σ and 2σ envelopes. Table S2. Inividual glass shard analyses in core MD07-3100. Major elements not normalized‚ analyzed by EPMA‚ trace elements analyzed by LA-ICP-MS. Table S3. Inividual glass shard analyses in core MD07-3098. Major elements, not normalized, analyzed by EPMA. Table S5.- Planktonic foraminifera radiocarbon ages from core MD07-3098 and the respective marine surface reservoir age correction applied (Rs) in the calibration.