The Indian Ocean has been proposed as an important source of salt for North Atlantic deep-water c... more The Indian Ocean has been proposed as an important source of salt for North Atlantic deep-water convection sites, via the Agulhas Leakage, and may thus drive changes in the ocean’s overturning circulation. However, while past changes in Agulhas leakage volume have been explored, little is known about this water’s salt content, representing a major gap in our understanding of Agulhas salinity supply. Here, we present new planktonic foraminiferal Mg/Ca-derived sea surface temperatures (SST) and stable isotope-derived salinity reconstructions for the last 1.2Ma from the western Indian Ocean source waters of the Agulhas Leakage to investigate glacial-interglacial changes in surface water properties. We find that SST and relative salinity both increase during glaciation, leading to high salinity and SST during glacial maxima. We show that the onset of surface salinification and warming in the Indian Ocean occurs during a phase of rapid land-bridge exposure in the Indonesian archipelago i...
Silicon isotope records from diatoms can be used as a proxy for the relative consumption of disso... more Silicon isotope records from diatoms can be used as a proxy for the relative consumption of dissolved silicic acid (DSi) in surface waters. Silicon isotopes in sponges provide information on the concentration of DSi within the ambient seawater in which the sponges reside. Here we provide deglacial silicon isotope records from both diatoms (d30Si_diat) and sponges (d30Si_sponge) collected in three piston cores from the Southern Ocean. Isolated diatom samples were produced from bulk sediment by mechanical separation and chemical cleaning. Pure diatom samples were digested in 0.1 M NaOH before removal of matrix via cation exchange chromatography. The samples were analysed by MC-ICP-MS at the University of Edinburgh. Sponge spicules were individually picked from sediment and underwent the same analytical procedure as decribed above. We relate the d30Si_diat records to changes in the deep upwelling DSi supply and diatom demand for DSi in the Southern Ocean surface across the deglaciation. We suggest that during the late deglaciation, the supply increased dramatically, leading to a decline in the d30Si_diat in all records. The d30Si_sponge data were used in conjunction with older previously published data to elucidate how a restructing of the deep ocean - which supplies DSi to the Southern Ocean - during the deglaciation, could explain the apparent increase in DSi supply that is recorded in the d30Si_diat data.
Changes in ocean circulation and the biological carbon pump have been implicated as the drivers b... more Changes in ocean circulation and the biological carbon pump have been implicated as the drivers behind the rise in atmospheric CO2 across the last deglaciation; however, the processes involved remain uncertain. Previous records have hinted at a partitioning of deep ocean ventilation across the two major intervals of atmospheric CO2 rise, but the consequences of differential ventilation on the Si cycle has not been explored. Here we present three new records of silicon isotopes in diatoms and sponges from the Southern Ocean that together show increased Si supply from deep mixing during the deglaciation with a maximum during the Younger Dryas (YD). We suggest Antarctic sea ice and Atlantic overturning conditions favoured abyssal ocean ventilation at the YD and marked an interval of Si cycle reorganisation. By regulating the strength of the biological pump, the glacial–interglacial shift in the Si cycle may present an important control on Pleistocene CO2 concentrations.
The Indian Ocean has been proposed as an important source of salt for North Atlantic deep-water c... more The Indian Ocean has been proposed as an important source of salt for North Atlantic deep-water convection sites, via the Agulhas Leakage, and may thus drive changes in the ocean’s overturning circulation. However, while past changes in Agulhas leakage volume have been explored, little is known about this water’s salt content, representing a major gap in our understanding of Agulhas salinity supply. Here, we present new planktonic foraminiferal Mg/Ca-derived sea surface temperatures (SST) and stable isotope-derived salinity reconstructions for the last 1.2Ma from the western Indian Ocean source waters of the Agulhas Leakage to investigate glacial-interglacial changes in surface water properties. We find that SST and relative salinity both increase during glaciation, leading to high salinity and SST during glacial maxima. We show that the onset of surface salinification and warming in the Indian Ocean occurs during a phase of rapid land-bridge exposure in the Indonesian archipelago i...
Silicon isotope records from diatoms can be used as a proxy for the relative consumption of disso... more Silicon isotope records from diatoms can be used as a proxy for the relative consumption of dissolved silicic acid (DSi) in surface waters. Silicon isotopes in sponges provide information on the concentration of DSi within the ambient seawater in which the sponges reside. Here we provide deglacial silicon isotope records from both diatoms (d30Si_diat) and sponges (d30Si_sponge) collected in three piston cores from the Southern Ocean. Isolated diatom samples were produced from bulk sediment by mechanical separation and chemical cleaning. Pure diatom samples were digested in 0.1 M NaOH before removal of matrix via cation exchange chromatography. The samples were analysed by MC-ICP-MS at the University of Edinburgh. Sponge spicules were individually picked from sediment and underwent the same analytical procedure as decribed above. We relate the d30Si_diat records to changes in the deep upwelling DSi supply and diatom demand for DSi in the Southern Ocean surface across the deglaciation. We suggest that during the late deglaciation, the supply increased dramatically, leading to a decline in the d30Si_diat in all records. The d30Si_sponge data were used in conjunction with older previously published data to elucidate how a restructing of the deep ocean - which supplies DSi to the Southern Ocean - during the deglaciation, could explain the apparent increase in DSi supply that is recorded in the d30Si_diat data.
Changes in ocean circulation and the biological carbon pump have been implicated as the drivers b... more Changes in ocean circulation and the biological carbon pump have been implicated as the drivers behind the rise in atmospheric CO2 across the last deglaciation; however, the processes involved remain uncertain. Previous records have hinted at a partitioning of deep ocean ventilation across the two major intervals of atmospheric CO2 rise, but the consequences of differential ventilation on the Si cycle has not been explored. Here we present three new records of silicon isotopes in diatoms and sponges from the Southern Ocean that together show increased Si supply from deep mixing during the deglaciation with a maximum during the Younger Dryas (YD). We suggest Antarctic sea ice and Atlantic overturning conditions favoured abyssal ocean ventilation at the YD and marked an interval of Si cycle reorganisation. By regulating the strength of the biological pump, the glacial–interglacial shift in the Si cycle may present an important control on Pleistocene CO2 concentrations.
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