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How the Central American Seaway Alters Large-Scale Ocean Circulation, Climate, and Marine Biogeochemistry
Wednesday, 17 January 2018, 12:00
Wednesday, January 17, 2018. 12:00PM. How the Central American Seaway Alters Large-Scale Ocean Circulation, Climate, and Marine Biogeochemistry. Lori Sentman. Sponsored by Geophysical Fluid Dynamics Laboratory. More information here.
The study of past climates using climate models and paleoclimate proxy records is helpful for understanding how the Earth system responds to external natural forcing on time scales longer than the current instrumental records. The Central American Seaway (CAS) was an important ocean gateway connecting the Pacific and Atlantic Oceans until its gradual shoaling and final closure near the end of the Pliocene (5.3-2.6 Ma), when paleoclimate proxy records indicate a major reorganization in large-scale ocean circulation and shifting spatial patterns in global climate and marine biogeochemistry. Climate models are inconsistent on the impact of the CAS on global deep-water circulation, tropical Pacific and Southern Hemisphere physical mean state, and interannual tropical Pacific climate variability, and have not explored the coupled impacts on ocean biogeochemistry or sediment calcium carbonate (CaCO3) long-term burial. A suite of four idealized experiments, including a very narrow (109 km-wide) channel, are performed for multi-millennial scale simulations using the Geophysical Fluid Dynamics Laboratory Earth System Model, GFDL-ESM2G, to explore the various stages of CAS constriction and shoaling on global ocean circulation, climate and marine biogeochemistry. The CAS in GFDL-ESM2G provides a shortcut for southern sourced Pacific water mass transport that warms the South Atlantic, reduces Indonesian Throughflow mass transport by 59- 82%, suppresses Antarctic Bottom Water northward extent, and allows North Atlantic Deep Water to deepen ~500 m and slightly strengthen (~2Sv). In response to the global ocean reorganization associated with the CAS opened to various shoaling stages, global mean surface air temperatures warm 0.4-0.7°C with a bipolar, asymmetric response of Northern Hemisphere cooling up to ~2°C in the northwest Pacific and Southern Hemisphere warming up to ~8°C near the Ross Sea, in contrast to global mean cooling in previous CAS climate modeling studies. Opening the CAS also leads to larger El Niño-Southern Oscillation (ENSO) amplitude with more La Niña or cold events, a weaker annual cycle, and ~3 months earlier development. Opening the CAS results in stronger ventilation and a reduction in the sequestration efficiency of the biological pump, allowing respired CO2 to escape to the atmosphere via increased ocean CO2 outgassing, a short-term (< 500 kyr) increase in global sediment CaCO3 (~200 PgC over 105 years), and an additional release of 238 ppmv (507 PgC) to the atmosphere from the partitioning of carbon species implying short-term warming of 0.4-1.0 K in the Pliocene with a very narrow CAS. Overall, this paleoclimate application has broad implications for the sensitivity of coupled ocean-atmosphere dynamics and ocean biogeochemistry to changing ocean circulation with far reaching, long-term climate, ENSO, marine ecosystem, ocean biogeochemical, and atmosphere pCO2 impacts.
Location NOAA GFDL, Smagorinsky Seminar Room, Princeton, NJ.