New Study Links Salinity Changes in the Gulf of Mexico to Changes in Rainfall Patterns in the Western Hemisphere

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The project is part of a collaborative effort to better understand how sea surface temperature and salinity have varied over the Holocene, or the past 10,000 years. The approach is to measure the magnesium to calcium ratios and oxygen isotopic composition in planktic foraminifera deposited on the seafloor.

This article is part of the February 2018 issue of the Sound Waves newsletter.

Map of globe with colors plotted to show long-term correlations between observed sea-surface salinity and rainfall.

Long-term correlations between observed sea-surface salinity and rainfall. Correlation map between northern Gulf of Mexico sea-surface salinity (SSS; dashed red box) and global oceanic SSS (ORA-S4 data set; red-blue scale), as well as continental precipitation (GPCC data set; brown-green scale) with locations of proxy records used in the study. Proxy locations are marked with circles (sedimentary records), triangles (speleothems), dashed boxes (tree-ring compilations), stars (circulation proxies), and squares (additional proxies) with color fill indicating sign (fresh–blue; dry/wet–brown/green; purple–weakened poleward transport) during the Little Ice Age (1450–1850 C. E.). Correlations were performed with 8-year lowpass filters to reduce sensitivity to interannual variability, where black stippling indicates significance at the 5% confidence level.

Sediment cores holding 4,000 years’ worth of climate history from the Gulf of Mexico were used to link Atlantic surface currents to rainfall over continents.

USGS scientists at the St. Petersburg Coastal and Marine Science Center, in collaboration with researchers at the Institute for Geophysics at University of Texas at Austin, have published a study in Nature Communications linking salinity changes in the Gulf of Mexico over the past 4 millennia to changes in rainfall patterns in the Western Hemisphere.

The project is part of a collaborative effort to better understand how sea surface temperature and salinity have varied over the Holocene, or the past 10,000 years. The approach is to measure the magnesium to calcium ratios (Mg/Ca) and oxygen isotopic composition (δ18O) in planktic foraminifera deposited on the seafloor. This technique is based on the principle that the Mg/Ca and δ18O in foraminifera vary as a function of temperature and salinity of surface waters, and are well-calibrated to these parameters using modern sediment trap studies. When sediment cores are collected from the deep ocean, the geochemistry of the foraminifera were analyzed to generate a decadally-resolved time series of surface ocean temperature and salinity variability spanning multiple millennia.

Salinity variability in the Gulf of Mexico is important, not only to understanding the regional climate of the Gulf, but this study argues that Gulf of Mexico salinity variations can be linked via the Gulf Stream to rainfall patterns on the continents bordering the Atlantic Ocean. The Gulf of Mexico serves as the headwaters to the Gulf Stream, the surface current that transports heat and salt from the tropical Atlantic to the high latitude North Atlantic Ocean, and is an important component of Atlantic Meridional Overturning Circulation (AMOC). Model projections indicate that the AMOC will weaken with increased greenhouse gas emissions, and thus understanding the long-term linkages between surface ocean circulation changes and precipitation patterns is important to projecting and preparing for these future changes in western hemisphere rainfall patterns.

One of the notable findings in this study is that during the Little Ice Age (1450–1850 A.D.), the Gulf of Mexico was significantly cooler and fresher, corresponding to documented rainfall anomalies in Africa, Europe, North America and South America. Using data-model comparisons, this study reveals that a weakening of the Gulf Stream and the entire AMOC system was the likely link between Little Ice Age conditions in the Gulf of Mexico and anomalies in Western Hemisphere rainfall patterns.

The full citation for the article is:

Thirumalai, K., Quinn, T.M., Okumura, Y., Richey, J.N., Partin, J.W., Poore, R.Z., Moreno-Chamarro, E., 2018, Pronounced centennial-scale Atlantic Ocean climate variability correlated with Western Hemisphere hydroclimate, Nature Communications, doi:10.1038/s41467-018-02846-4.

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Date published: February 28, 2018

Sound Waves Newsletter - February 2018

Researchers find giant grooves on the tectonic plates that form a subduction zone, impacts of climate change may make many low-lying Pacific islands uninhabitable in 20 years, how two recent earthquakes did not trigger larger tsunamis, a new data catalog that makes it easier to find coastal and marine data sets, and more in this February 2018 issue of Sound Waves.