Caribbean Surface Water Research Articles

Biogeography of Neogene calcareous nannofossils in the Caribbean and the eastern equatorial Pacific—floral response to the emergence of the Isthmus of Panama

Principal components analysis of nannofossil assemblages in five ODP sites in the Caribbean and the eastern equatorial Pacific was used to monitor Neogene surface water circulation changes. In 15.83–10.71Ma, floral distributions clearly show the existence of the Circum-tropical Current between the Caribbean and the eastern equatorial Pacific and no surface water communication between the northern and southern Caribbean. In 10.71–9.36Ma, the Circum-tropical Current weakened and the northward intra-Caribbean current had been initiated. Northern and southern Caribbean surface waters again became separated in 8.35–3.65Ma and the Circum-tropical Current was regenerated. After 2.76Ma, the northward intra-Caribbean current has completely been established and the Circum-tropical Current disappeared. This suggests that a barrier to the Circum-tropical Current had formed, indicating the final closure of the Isthmus of Panama.

Upwelling on the Yucatan Shelf: hydrographic evidence

Hydrographic data gathered during four cruises are used to evidence upwelling on the Yucatan Shelf, and describe its structure. Subsurface Caribbean water (characterized by 16 to 20°C, 36.1 to 36.5 S, and 8 to 14 μmol 1 −1 nitrate concentrations) upwells along the eastern slope of the Yucatan Shelf. This water, which originates at depths of about 220–250 m in the Yucatan Channel, rises at about 10 −2 cm s −1 to dome into the euphotic zone, but only occasionally breaks the ocean surface. This upwelling appears to follow a seasonal cycle. During spring and summer the upwelled water intrudes over the Yucatan Shelf to create a two-layered water column. Strong stratification between Caribbean surface water (CSW) and the Yucatan upwelling water (YUW) layer on the shelf is likely to prevent mixing between them, except during the winter periods of northern winds. The YUW layer moves westward across the shelf and contributes to the formation of a cyclonic gyre north of Cape Catoche. The curl of the prevailing wind stress is not likely to induce upwelling along the eastern Yucatan slope. The observations imply that the upwelling is probably caused by bottom friction or other topographical mechanisms. A subsurface countercurrent runs southward along the eastern slope of the Yucatan Shelf, and appears to be closely related to the upwelling process. The Salinity Maximum is ruptured on the western side of the Yucatan Channel as a consequence of the upwelling. The data presented support the hypothesis that Yucatan is one of the most important upwelling regions on a western oceanic margin.

Tracing the Amazon component of surface Atlantic water using 228Ra, salinity and silica

High 228Ra/226Ra activity ratios characteristic of waters in the Amazon estuary provide a sensitive indicator of the presence of these waters in the Atlantic Ocean. A conservative mixing model utilizing the 228Ra/226Ra activity ratio (AR) tied to absolute measurements in the estuary allows us to estimate that 20–34% of the surface water east of the Antilles during June, 5–9% from the same area during December, and 15–20% of the eastern Caribbean surface water during December are derived from the Amazon estuary. Differences in 228Ra input occur in response to variable stratification of water near the river mouth. During high discharge, intense vertical mixing enriches the water in the estuary in 228Ra. A large fraction of this water moves to the north and east of the Antilles, where its relatively high 228Ra/226Ra AR distinguishes it over 1500 km from its source. During low discharge (northern hemisphere fall) a significant fraction of river water passes northwest of the zone of intense mixing into a vertically stratified region where 228Ra gain is lower. This water is transported by the Guiana Current along the coast of South America and into the Caribbean.

Evidence of coastal Seiche excitation by tide‐generated internal solitary waves

Coastal seiches at Magueyes Island, Puerto Rico, occur in distinct fortnightly groups with maximum seiche activity following new and full moon by 7 days. The size of the fortnightly groups depends upon the amplitude of the preceding spring tide and upon the Caribbean surface water temperature. Temperature records from the upper thermocline on the slope seaward of the shelf edge off Magueyes Island indicate the arrival of semidiurnal packets of negative internal solitary waves. We suggest that these internal waves are generated by tides in the southeastern Caribbean Sea and that they are responsible for exciting the coastal seiches. This hypothesis is supported by the characteristics of coastal seiching at Puerto Princesa on Palawan Island in the Philippines which indicate excitation by the Sulu Sea internal waves reported by Apel, Holbrook and Tsai (1980).

Isotopic Paleoceanography of the Caribbean and East Pacific: Role of Panama Uplift in Late Neogene Time

Comparisons of carbon isotopic data on benthic foraminifera from Deep Sea Drilling Project sites 502 (western Caribbean) and 503 (eastern Pacific) indicate that the difference between the Atlantic and the Pacific in the per mil enrichment in carbon-13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago, when the difference reached the modern level (1 per mil). Comparisons of planktonic foraminiferal oxygen isotopic data for the Caribbean and the Pacific suggest that the salinity of Caribbean surface waters began increasing 4 million years ago, possibly in response to shoaling of the Panama isthmus. These results suggest that modern circulation patterns in the Caribbean and eastern Pacific developed by 3 million years ago in concert with changing tectonic, climatic, and biogeographic patterns.

Volatile liquid hydrocarbons in waters of the Gulf of Mexico and Caribbean Sea1

Concentrations of volatile liquid hydrocarbons (VLH), C6−C14 hydrocarbons, were determined in 1977 in coastal, shelf, and open‐ocean surface waters of the Gulf of Mexico and Caribbean Sea. In open‐ocean, nonpetroleum‐polluted surface water, VLH concentrations were 60 ng·liter−1 while in heavily polluted Louisiana shelf and coastal water values reached ≈500 ng·liter−1. Caribbean surface samples had very low concentrations, ≈30 ng·liter−1. The relationship between anthropogenic gaseous hydrocarbons and VLH was approximately linear. Aromatic VLH accounted for 60–85% of the total VLH in surface waters. Cycloalkane concentrations were <1.0 ng·liter−1 in open ocean water, 60–100 ng·liter−1 in polluted water (20% of total VLH). Alkanes were ≈15 ng·liter−1 in open ocean water, 40 ng·liter−1 in polluted water. The concentrations of five major VLH compounds (aromatics) in water samples—benzenc, toluene, ethylbenzene, m‐, p‐xylenes, and o‐xylene (called BTX)— were sufficient to predict the total VLH. The empirically determined relationship is VLH(ng·liter−1) = 1.42 BTX (ng·liter−1); r = 0.96.Subsurface VLH concentrations in samples of polluted waters collected from depths of 50 in were only 35–40 ng·liter−1 below surface concentrations. Open ocean subsurface samples had concentrations of only ≈30 ng·liter−1 at 30–50‐m depths, comparable to those of Caribbean surface water.