Project Details
Projekt
Defining the late Anthropocene response of the Eastern Tropical Pacific Oxygen Deficient Zone to climate change (ANTHR-ODZ)
Applicant
Dr. Alan Foreman
Subject Area
Oceanography
Term
since 2026
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 569202185
There has been an increasing recognition that the oxygen content of the world’s oceans is decreasing as a result of climate change. Climate models consistently predict that this trend will continue or even accelerate as global oceans warm, albeit with mixed agreement as to the location and magnitude of such reductions. Defining observations by which we can evaluate and improve these model predictions is thus of paramount importance. This is particularly true of the areas of the ocean where there is little or no oxygen (Oxygen Deficient Zones, or ODZs), as the sensitivity of macroorganisms to low oxygen concentrations is highly nonlinear. Beyond their direct biological impact, ODZs are also a source of food and economic security for millions of people in the tropics because of the highly productive surface conditions associated with their formation. Just as important, ODZs regulate climate by modulating the marine nitrogen (N) cycle (itself linked to the global carbon cycle) and via the production of the greenhouse gas nitrous oxide. Given their importance, understanding how ODZs have evolved over the 20th and 21st centuries is key to predicting their response to future climate change. Yet the uncertainties and complex feedbacks involved in their formation have made modelling this behavior difficult, and in situ observations of ODZ regions are of limited use due to their poor temporal resolution. Traditionally, paleo-oceanographers have circumvented this hurdle by analyzing chemical changes in microfossils collected from sediments. This is not possible in the case of the Anthropocene, however, because sediments lack the temporal resolution required to capture annual and decadal variability in climate signals and may be subject to diagenetic alteration that can bias reconstructions of ODZ dynamics. These problems can be overcome via the chemical analysis of scleractinian reef-building corals, which have been shown to be reliable recorders of ocean conditions, and which grow quickly enough that seasonal resolution can be achieved. Here I propose to create 50-year records of the N isotope composition of coral skeletal organic matter collected from 6 sites spanning the Eastern Tropical North Pacific (ETNP), the world’s largest ODZ. Such N isotope ratios are sensitive to the extent of water column denitrification, a process only present in ODZs. Taken together, this network of corals will record any fluctuations in the ETNP ODZ since the 1970s. I will pair these observations with reconstructions of sea surface temperature from the same corals to better elucidate the mechanisms driving any changes I observe. This project will thus define when, how, and why the world’s largest ODZ has changed since the 1970s, a crucial gap in our understanding with regard to how ODZs will evolve in the future.
DFG Programme
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