A Multi-Proxy Approach to Reconstructing Late Holocene Ocean Conditions in the Gulf of Maine and the Northwestern Atlantic
The Gulf of Maine is warming faster than than 99% of the rest of the world's oceans. Understanding the causes of this warming and the natural variability of the system requires reconstructing past ocean conditions in the region. We are using multiple geochemical proxies, including oxygen, nitrogen, and radiocarbon isotopes, from Arctica islandica shells collected in the western Gulf of Maine to reconstruct oceanic conditions over the last several centuries. Related Publications: Lower-Spies et al., 2020, Journal of Geophysical Research - Oceans.
Bulk and CSIA-AA Nitrogen Isotopes of Shell Periostracum
Along with our colleagues at Bates College (Lewiston, ME), we have been investigating the utility of periostracum (the protein rich layer on the outside of shells) as a proxy for baseline nitrogen isotopes of nitrate and water mass source changes. Using both bulk nitrogen isotopes and compound specific nitrogen isotopes of amino acids, we have shown that periostracum records the nitrogen isotopes of the clam's food source and that the diet of the clams we study in the Gulf of Maine has not change significantly in the last several centuries, making nitrogen isotopes of periostracum and reliable proxy of past nitrogen isotopes conditions. Future work will investigate changes in nitrogen isotopes in the northwestern North Atlantic over the last several hundred years to reconstruct water mass and ocean current changes. Related Publications: Whitney et al., 2019, Geochimica et Cosmochimica Acta.
Gulf of Maine Seawater Chemistry
In order to accurately interpret the paleoceanographic data we obtain from oceanographic proxies, we first have to gain a better understanding of what different geochemical signatures tell us about modern ocean conditions. To this end, we have collected hundreds of water samples from both surface coastal areas as well as deep basins throughout the Gulf of Maine. Using temperature, salinity, oxygen isotopes, and nitrogen and oxygen isotopes of dissolved nitrate, we can define the location and origin of different water masses as well as the nitrogen cycling and mixing that occurs within and between them. Related Publications: Whitney et al., 2017, Continental Shelf Research; Whitney et al., 2020, Continental Shelf Research.