Accomplished Based Renewal: A Glacial Age Synthesis of Western North Atlantic Hydrography

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In the present day, warm and salty near surface waters of Gulf Stream origin are transported to high latitudes where they give up their heat and warm northeast Europe. At the same time the surface waters become denser and exit the Nordic (Greenland, Iceland, and Norwegian) Seas and over about 1000 years spread to other parts of the ocean. This process was interrupted during glacial times because the Nordic Seas were freshened by water from nearby ice sheets, and climate in Europe was more like Greenland today. As a result, it is often thought that deep ocean circulation was “off” during glaciation, and “on” during interglacial climate. Considering the size and climate impact of deep ocean circulation, the deep ocean is poorly sampled. For example, only recently it was found that at depths greater than 5000 m there was a dense, salty water that must have been produced in the Nordic or Labrador Seas during glacial times. So now it can be stated that the glacial circulation was probably never “off.” This project will increase the existing database of glacial-age sediment properties from the western subtropical North Atlantic by about 30 percent, and that in turn will lead to a first three-dimensional picture of the “state” of the glacial ocean where the export of heat, salt, nutrients, and carbon dioxide can be modeled and quantified.To accurately reconstruct past changes in deep water circulation requires a wide distribution of stable isotope (d18O and d13C) measurements and radiocarbon dates on microscopic fossil shells from deep sea sediment cores at various locations and depths. These cores were collected by the Principal Investigator on research cruises from 1994, 1998, 2004, 2010, 2017, 2019, and 2021 and new data will be developed for a dozen of them. The stable isotopes are proxies for deep ocean temperature, salinity and CO2 content, and radiocarbon data from plankton will be used to identify the last glacial maximum (about 20,000 years ago) as well as act as a tracer for the age of the deep water in shells of bottom dwelling microfossils. In addition, the glacial maximum data compilation will include cores from the upper 2 km of the western North Atlantic, where there are few data, but very strong gradients in paleo properties are indicative of salinity, temperature, nutrients, and transport in Glacial North Atlantic Intermediate Water. The synthesis data will be useful for studying the ocean’s capacity to store and transport heat, salt, and nutrients and will be used to validate climate models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.