Physics
Scientific paper
Aug 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004e%26psl.224..493b&link_type=abstract
Earth and Planetary Science Letters, Volume 224, Issue 3-4, p. 493-507.
Physics
16
Oxygen Isotopes, Salinity, Tropical Meteorology, Panama Bight
Scientific paper
Westward transport of freshwater across the Panama Isthmus helps to maintain the salinity (S) contrast between the Atlantic and Pacific Oceans, important in global thermohaline circulation and climate. Relatively low sea-surface salinities in the Panama Bight reflect high net precipitation. We infer sources of this freshwater input to the region based on oxygen isotopes (δ18O) of precipitation (δP) and seawater (δSW). The primary trend of the surface water δSW-S relationship implies a freshwater endmember δ18O of -8.5+/-0.3‰, significantly lower than the mean δP of rainwater we measured in the region (-4.8+/-1.8‰), mixing with waters upwelled from the subsurface (S=34.9-35.1 PSU, δSW=0.3-0.4‰). Based on limited isotope and salinity data, these upwelling waters are a mixture of ~60% tropical waters and ~40% subtropical mode waters. Three secondary trends in the surface water δSW-S distribution point to similar freshwater sources with δ18O of -2.5+/-1.2‰, -4.7+/-0.5‰, and -4.8+/-0.6‰, consistent with local precipitation sources. Accounting for the primary surface water trend, intermittent cross-isthmus transport of moist air masses from the Caribbean may introduce relatively 18O-depleted rainfall due to a combination of recycling and orographic distillation. In addition, relatively infrequent but large tropical storms, which may contain freshwater of both Pacific and Caribbean origin, deliver rainfall with δP of -10‰ to -14‰. The primary trend of regional surface seawater data, which integrates the different sources over time, suggests that about half of the total precipitation reflects local sources, and half reflects a combination of cross-isthmus transport and large storms. The regional δSW-S distribution is sensitive to the relative contributions of these freshwater sources, which may change under different climate regimes.
Benway Heather M.
Mix Alan C.
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