ALBERT

Description: This study tests the hypothesis that the late Miocene to early Pliocene constriction and closure of the Central American Seaway (CAS), connecting the tropical Atlantic and East quatorial Pacific (EEP), caused a decrease in productivity in the Caribbean, due to decreased coastal upwelling and an end to the connection with high-productivity tropical Pacific waters. The present study compared paleoceanographic proxies for the interval between 8.3 and 2.5 Ma in 47 samples from south Caribbean ODP Site 999 with published data on EEP DSDP Site 503. Proxies for Site 999 include the relative abundance of benthic foraminiferal species representing bottom current velocity and the flux of organic matter to the sea floor, the ratio of infaunal/epifaunal benthic foraminiferal species and benthic foraminifer accumulation rates (BFARs). In addition, we calculated % resistant planktic foraminifers species and used the previously published % sand fraction and benthic carbon isotope values from Site 999. During early shoaling of the Isthmus (8.3-7.9 Ma) the Caribbean was under mesotrophic conditions, with little ventilation of bottom waters and low current velocity. The pre-closure interval (7.6-4.2 Ma) saw enhanced seasonal input of phytodetritus with even more reduced ventilation, and enhanced dissolution between 6.8 and 4.8 Ma. During the post-closure interval (4.2-2.5 Ma) in the Caribbean, paleoproductivity decreased, current velocity was reduced, and ventilation improved, while the seasonality of phytodetrital input was reduced dramatically, coinciding with the establishment of the Atlantic-Pacific salinity contrast at 4.2 Ma. Our data support the hypothesis that late Miocene constriction of the CAS at 7.9 Ma and its closure at 4.2 Ma caused a gradual decrease in paleoproductivity in the Caribbean, consistent with decreased current velocity and seasonality of the phytodetrital input.

Description: Diversity trends 8.3-2.5 Ma in Caribbean deep-sea foraminifera, as interpreted from the indices Fisher's alpha and the Information Index [H(S)] parallel paleoproductivity proxies (benthic foraminiferal infaunal/epifaunal species ratio, benthic foraminifer accumulation rates and flux of organic carbon to the seafloor). Paleoproductivity never reached an eutrophic threshold value above which we would predict opposite trends of high paleoproductivity and low diversity, consistent with stressful conditions. Instead, results are similar to those from other studies of oligotrophic settings that show a positive and statistically significant correlation between paleoproductivity and diversity. The correlations between current intensity and watermass oxygenation with diversity are negative and statistically significant. These results are also borne out by Principal Component Analysis (PCA). Intervals of increased relative abundance of Epistominella exigua, a proxy for seasonality of phytodetrital input to the seafloor, coincide with increased diversity, suggesting that pulsed paleoproductivity enhanced the diversity signal in the Caribbean. Diversity and paleoproductivity peaked in the Caribbean at 7.9 Ma, and declined thereafter due to the cut off of the nutrient-rich Pacific deep waters (〈1000 m) into the Caribbean. From 7.6 to 4.2 Ma, both diversity and paleoproductivity increased. With the complete closure of the Caribbean-Pacific seaway at 4.2 Ma, both diversity and paleoproductivity gradually decreased from a high at 4.2 Ma to moderate values until the end of the study interval at 2.5 Ma. Major intervals of significant shifts in Caribbean diversity and paleoproductivity were also confirmed with SHEBI analysis that displays a diverging trend between the Pacific and Caribbean sites since 7.9 Ma, with the Caribbean displaying decreasing values. In summary, in the Caribbean, decreased paleoproductivity due to the gradual constriction and the final closure of the Central American Seaway (CAS) led to decreased deep-sea benthic foraminiferal diversity and that both benthic foraminiferal diversity and paleoproductivity maintained a positive relationship.

Description: We collected pelagic sediments from Holes A and B of IODP Site 342-U1407 that accumulated on the Southeast Newfoundland Ridge that spanned the Early Cenomanian to Early Turonian. In this study, we reconstruct the paleoceanographic changes before, during, and after Oceanic Anoxic Event 2 (OAE2) to isolate the triggers behind the widespread deposition of organic matter (OM) during this time. We combined the stable isotopes of bulk organic carbon, total organic carbon, total inorganic carbon, major and trace elements, and abundances of microfossils (benthic foraminiferal, biserial heterohelicid foraminifera, and radiolarians) to characterize the sediments. Biomarker indices were also calculated to determine the source and thermal maturity of the OM.

Description: Analyses of 203 samples of benthic foraminifera in six cores from four sites in Florida Bay indicate habitat change over the last ~4000 years. Sample ages were determined for the last ~120 years with 210Pb, and for up to ~4000 years at two sites with 14C. The largest habitat changes upcore were identified with stratigraphically constrained cluster analysis (CONISS), which evaluates the similarity of vertically adjacent samples. Paleoenvironmental interpretations of habitat changes were mostly based on varying proportions of two defined associations of environmental indicator taxa and changes in diversity. The timing of the interpreted environmental changes was compared to known natural and anthropogenic events to examine their correspondence and possible relationship.The bay’s initial flooding ~4000 YBP was indicated at the offshore Ninemile Bank by a very high proportion of an Ammonia association and very low proportion of a Quinqueloculina association, similar to modern nearshore assemblages in Trout Cove, the core site closest to the mainland. Construction of the Florida Keys railroad in 1907–1910 led to restricted exchange with the open ocean; foraminifera indicate a salinity decrease at that time, probably from the increased influence of runoff. Faunal changes since the 1920s in central Florida Bay signify increasingly saline (〉32 psu) waters. Between 1928–1938, concurrent peaks in the Ammonia association at all sites suggest widespread freshening of the bay, which corresponds to an unusual succession of three powerful, wet hurricanes between 1926–1938. After flushing of the bay by hurricanes, a long-term result of decreased circulation caused by railroad construction was the increased retention of organic materials in the bay; more organic-rich conditions after 1932 are indicated at Ninemile Bank by a shift in infaunal Bolivina species to their highest abundance. In the central bay after 1962, the amplitude of changes in the Ammonia association and diversity was greater, probably related to larger salinity shifts caused by increases in water management in addition to natural events such as droughts. In the central bay in 1987, decreases in diversity, increases in infaunal taxa and decreases in epiphytic species clearly reflect a severe, bay-wide seagrass die-off and drought. Thus, changes in Florida Bay habitats can be related to both anthropogenic and natural causes. Despite any degradation of water quality in the past 50 years, foraminiferal diversity has increased at most sites.