Farmer Jesse R.

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Last Name
Farmer
First Name
Jesse R.
ORCID
0000-0001-5200-6429

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  • Article
    Bioactive trace metals and their isotopes as paleoproductivity proxies: an assessment using GEOTRACES-era data
    (American Geophysical Union, 2021-05-24) Horner, Tristan J. ; Little, Susan ; Conway, Tim M. ; Farmer, Jesse R. ; Hertzberg, Jennifer ; Janssen, David J. ; Lough, Alastair ; McKay, Jennifer L. ; Tessin, Allyson C. ; Galer, Stephen J. G. ; Jaccard, Samuel L. ; Lacan, Francois ; Paytan, Adina ; Wuttig, Kathrin
    Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate history.
  • Article
    Western Arctic Ocean temperature variability during the last 8000 years
    (American Geophysical Union, 2011-12-17) Farmer, Jesse R. ; Cronin, Thomas M. ; de Vernal, Anne ; Dwyer, Gary S. ; Keigwin, Lloyd D. ; Thunell, Robert C.
    We reconstructed subsurface (∼200–400 m) ocean temperature and sea-ice cover in the Canada Basin, western Arctic Ocean from foraminiferal δ18O, ostracode Mg/Ca ratios, and dinocyst assemblages from two sediment core records covering the last 8000 years. Results show mean temperature varied from −1 to 0.5°C and −0.5 to 1.5°C at 203 and 369 m water depths, respectively. Centennial-scale warm periods in subsurface temperature records correspond to reductions in summer sea-ice cover inferred from dinocyst assemblages around 6.5 ka, 3.5 ka, 1.8 ka and during the 15th century Common Era. These changes may reflect centennial changes in the temperature and/or strength of inflowing Atlantic Layer water originating in the eastern Arctic Ocean. By comparison, the 0.5 to 0.7°C warm temperature anomaly identified in oceanographic records from the Atlantic Layer of the Canada Basin exceeded reconstructed Atlantic Layer temperatures for the last 1200 years by about 0.5°C.