DOI: 10.25921/63q4-y607
title: NOAA/WDS Paleoclimatology - Holocene Variations in Subtropical Atlantic SST

description: A faunal record of sea-surface temperature (SST) variations off West Africa documents a series of abrupt, millennial-scale cooling events, which punctuated the Holocene warm period. These events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling. The most recent of these events was the Little Ice Age, which occurred between 1300 to 1850 A.D., when subtropical SSTs were reduced by 3° to 4°C. These events were synchronous with Holocene changes in subpolar North Atlantic SSTs, documenting a strong, in-phase link between millennial-scale variations in high- and low-latitude climate during the Holocene.
description: Holocene SST variations at Site 658C were reconstructed using planktonic foraminiferal assemblage data. Ocean Drilling Program Hole 658C was cored off Cap Blanc, Mauritania (20°45'N, 18°35'W, (GPS), 2263m) during ODP Leg 108. Sediment accumulation rates are high at this site (22 cm/kyr average) due, in part, to the dual influences of high regional surface ocean productivity and high supply of windblown African mineral dust. Strong seasonal upwelling and high productivity results from the strong northeast Trade winds which parallel the Northwest African margin. Hole 658C is also positioned within the axis of the summer African eolian dust plume which transports Saharan mineral aerosol dust to the adjacent subtropical Atlantic ocean. The site lies within an oceanographic boundary separating cooler temperate and subpolar waters to the north from warmer tropical water masses to the south and west. Core 1H from Hole 658C was continuously subsampled at 2 cm intervals which is equivalent to between 50-100 years temporal resolution. Samples were analyzed for calcium carbonate and biogenic opal percentages, and the residual terrigenous (eolian) fraction was computed by difference. Counts of 29 planktonic foramineferal species were converted to warm and cold season SSTs using the F13' transfer function derived from faunal analysis of 191 Atlantic core tops (Ruddiman and Glover, Quat. Res. 5, 361-389 1975). Standard errors of estimate for the F13'-derived warm and cold season SSTs are 1.6°C and 1.3°C, respectively. At Hole 658C, the coretop (0-2cm) warm and cold season foraminiferal SST estimates (16.8°C and 25.8°C) agree within the error of estimate with the observed annual SST range at this location (18°C and 24°C, respectively). Age control was established using 31 accelerator mass spectrometer (AMS) radiocarbon dates of monospecific samples of planktonic foraminifera (Globigerina bulloides or Globorotalia inflata) spanning the last 24,000 calendar years BP. Raw radiocarbon dates were converted to calibrated calendar ages after applying a -500±50 year reservoir correction. The resulting age-depth profile indicates that sedimentation was continuous at a rate of 22 cm/ka spanning the last ca. 14 cal. ka BP. However, a brief hiatus between 328-324 cm (17.4-14.3 cal. ka BP) is indicated by several closely spaced dates (19). Date of data generation: 1998-2000