Abstract
AbstractOver the past several decades, oxygen minimum zones have rapidly expanded due to rising temperatures raising concerns about the impacts of future climate change. One way to better understand the drivers behind this expansion is to evaluate the links between climate and seawater deoxygenation in the past especially in times of geologically abrupt climate change such as the Palaeocene‐Eocene Thermal Maximum (PETM), a well‐characterized period of rapid warming ~56 Ma. We have developed and applied the novel redox proxies of foraminiferal Cr isotopes (δ53Cr) and Ce anomalies (Ce/Ce*) to assess changes in paleoredox conditions arising from changes in oxygen availability. Both δ53Cr and Cr concentrations decrease notably over the PETM at intermediate to upper abyssal water depths, indicative of widespread reductions in dissolved oxygen concentrations. An apparent correlation between the sizes of δ53Cr and benthic δ18O excursions during the PETM suggests temperature is one of the main controlling factors of deoxygenation in the open ocean. Ocean Drilling Program Sites 1210 in the Pacific and 1263 in the Southeast Atlantic suggest that deoxygenation is associated with warming and circulation changes, as supported by Ce/Ce* data. Our geochemical data are supported by simulations from an intermediate complexity climate model (cGENIE), which show that during the PETM anoxia was mostly restricted to the Tethys Sea, while hypoxia was more widespread as a result of increasing atmospheric CO2 (from 1 to 6 times preindustrial values).
Highlights
As emitted greenhouse gasses accumulate in the atmosphere, temperatures are rising in both the atmosphere and the oceans with unclear consequences for marine ecosystems (Pörtner et al, 2014)
Our geochemical data are derived from three sites drilled by the Deep Sea Drilling Program (DSDP) and Ocean Drilling Program (ODP): DSDP Site 401 is located in the Bay of Biscay with a paleodepth of 1,900 m, ODP Site 1263 is on Walvis Ridge with a palaeodepth of 1,500 m, and ODP Site 1210 is on Shatsky Rise (North Pacific) with a palaeodepth of 2,400 m (Figure 1; Pälike et al, 2014, and references therein)
No Cr isotope data are available for the onset of the Palaeocene‐Eocene Thermal Maximum (PETM) itself as this was an interval of intense dissolution
Summary
As emitted greenhouse gasses accumulate in the atmosphere, temperatures are rising in both the atmosphere and the oceans with unclear consequences for marine ecosystems (Pörtner et al, 2014). One of the hazards associated with global warming is a decrease in oceanic dissolved oxygen content. Over the past 50 years O2 levels have been steadily declining, leading to the expansion of so‐called oxygen minimum zones—areas of hypoxic to suboxic levels of O2 at intermediate water depths due to the decreased solubility of O2 and increased metabolic rates of heterotrophic microbes as temperatures rise (Keeling et al, 2010). Understanding the effect of ocean warming on the expansion and intensification of oxygen minimum zones and deep ocean hypoxia is needed (Pörtner et al, 2014). We assess the development of ocean hypoxia under high temperatures by using extreme warming in the geological past as an analogue for modern anthropogenic warming. The injection of large amounts of carbon resulted in a decrease in alkalinity and intense dissolution of CaCO3
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
