No abstract

The Holocene is considered a period of relative climatic stability, but significant proxy data-model discrepancies exist that preclude consensus regarding the postglacial global temperature trajectory. In particular, a mid-Holocene Climatic Optimum,~9,000 to~5,000 years BP, is evident in Northern Hemisphere marine sediment records, but its absence from model simulations raises key questions about the ability of the models to accurately simulate climate and seasonal biases that may be present in the proxy records. Here we present new mid-Holocene sea surface temperature (SST) data from the western tropical Atlantic, where twentieth-century temperature variability and amplitude of warming track the twentieth-century global ocean. Using a new coral thermometer Sr-U, we first developed a temporal Sr-U SST calibration from three modern Atlantic corals and validated the calibration against Sr-U time series from a fourth modern coral. Two fossil corals from the Enriquillo Valley, Dominican Republic, were screened for diagenesis, U-series dated to 5,199 ± 26 and 6,427 ± 81 years BP, respectively, and analyzed for Sr/Ca and U/Ca, generating two annually resolved Sr-U SST records, 27 and 17 years long, respectively. Average SSTs from both corals were significantly cooler than in early instrumental and late instrumental periods at this site, by~0.5 and~0.75°C, respectively, a result inconsistent with the extended mid-Holocene warm period inferred from sediment records. A more complete sampling of Atlantic Holocene corals can resolve this issue with confidence and address questions related to multidecadal and longer-term variability in Holocene Atlantic climate.

No abstract

SummaryOrganic loading under a submerged fish cage in commercial operation has been quantified for the first time in the open ocean. Sediment traps out to 100 m sampled the loading continuously over the 15 months of a complete grow-out cycle for cobia (Rachycentron canadum). Typically 4% or 5% of the feed arrived directly to the sediment, although this benthic percentage became much higher in the last two months of this study. Almost all the loading (90%) lands within 30 m of the cage mooring block. The loading consists of fragments of feed pellets that wash out from the mouths and gills of the fish. The fragments sink rapidly and almost vertically; they are not carried horizontally into large dilution volumes. Dispersal on the sediment surface is much more extensive than dispersal in the water. This study developed expeditious and cost-effective techniques for sampling and analyzing organic loading, using a minimum of technological resources.

No abstract