Long-Term Variability and Trends in the Caribbean Sea

Upper ocean conditions in the Caribbean Sea are studied for long-term variability and trends using filtered surface observations and ocean model reanalysis fields. A principal component analysis is made, and trends in the leading mode are extracted. Sea surface temperature shows an accelerating upward trend while air pressure exhibits quasidecadal fluctuations. Sea surface height and subsurface temperature rise linearly while subsurface salinity exhibits fresher upper and saltier lower layers. The amplitude of warming is highest in the southern Caribbean east of 75°W near 150？m and lowest near the surface, indicating little role for a top-down process such as air-sea exchange. The freshening surface layer does not appear connected to river discharge or regional rainfall, so changes in ocean advection and sources are the likely drivers. Westward currents exhibit a reduction of throughflow and an influx from the Windward Passage. The Caribbean Current has slowed ~0.06？m/s in the reanalysis era. Crop yields show little sensitivity to ocean conditions but tend to follow rainfall. Marine catch per capita in the Caribbean follows subsurface currents and vertical motion but is less affected by temperature and salinity. 1. Introduction The accumulation of greenhouse gases and consequent absorption of radiation has resulted in an atmospheric warming that is faster in the Caribbean than elsewhere in the tropics. This is related to a local acceleration of the Hadley cell and gas plumes that drift west from Africa [1], producing a drying trend that is projected to continue in the 21st century [2]. How the sub-surface ocean contributes to global warming has recently been explored using observed temperature profiles and ocean model projections [3]. Across the central Antilles, the rate of warming at the top of the atmospheric boundary layer is triple the ocean surface, so sensible heat fluxes are declining. This has implications for the thermodynamic energy available to tropical weather systems within the region [4] and to the advection of heat, moisture and momentum out of the region. The Caribbean Sea is bounded on the south and west by South and Central America, and fringed on the east and north by the chain of Antilles Islands (8°N–25°N, 85°W–55°W) and Atlantic Ocean. Persistent subtropical trade winds, year-round sunshine, and consistent water exchanges result in little seasonal variation. The surface warm layer is >100？m deep and the upper 1200？m is stratified [5, 6]. Most Atlantic water infiltrates the Caribbean Sea through the Grenada, St. Vincent, and St.