Publication Date:
2024-01-09
Description:
We analyzed the unsaturation ratio (Uk37) of long-chain ketones - a molecular sea-surface temperature (SST) indicator û concentrations of carbonate and organic carbon in sediments from Site 846 in the eastern equatorial Pacific Ocean. Based on an isotopic age model for the composite depth section of 0-46 m below seafloor and on estimates of sediment density, accumulation rates of these biogenic compounds were calculated. Our combined temperature and biogenic flux record traces conditions at the origin of the South Equatorial Current over the last 1.3 m.y.
SSTs have fluctuated considerably over the interval studied. A long trend of gradual decrease from 24°C at 1.3 Ma ends between 500 and 400 Ka, when lowest values of 19°C were reached. Since this time, the temperature data indicate a warming trend to the Holocene modulated by high-amplitude variation (19° to 27°C). The inversion of the trend between 400 and 500 Ka coincides with maximal accumulation rates of carbonate, which since then have decreased. In contrast, organic carbon accumulation since then has increased in variability and in absolute values.
On shorter time scales, the records show a strong link to the global climatic background. Since 1.3 Ma, carbonate (0.2-3 g/cm**2/k.y.) and organic carbon accumulation rates (2-30 mg/cm**2/k.y.) were consistently high (more than twice their modern values and those of interglacials) during glacial maxima in the benthic isotope record, when temperatures were low.
However, cross-spectral analyses with the d18O record suggest that variation in organic carbon flux is not linked directly to variations in SST. Temperature maxima in our record led interglacial events by 7 k.y. in the 100-k.y. eccentricity cycle and by 5 k.y. in the 41-k.y. obliquity cycle. In contrast, maxima in organic carbon accumulation lag behind glacial maxima and low temperatures by 14 k.y. in the eccentricity cycle. On glacial/interglacial time scales, a prominent influence on SST - but not on organic carbon burial - at Site 846 appears to be the advection of cold water into the South Equatorial Current.
Keywords:
138-846; Accumulation rate, calcium carbonate; Accumulation rate, mass; Accumulation rate, total organic carbon; AGE; Alkenone, unsaturation index UK37; Calcium carbonate; Calculated; Calculated from UK37 (Prahl et al., 1988); Carbon, organic, total; Carbon, organic, total, standard deviation; Carbon, total; COMPCORE; Composite Core; Density, dry bulk; Density, wet bulk; Depth, composite revised; DEPTH, sediment/rock; DSDP/ODP/IODP sample designation; Element analyser CHNS-O, Carlo Erba EA1108; Gamma-ray attenuation porosity evaluator (GRAPE); Intercore correlation; Joides Resolution; Leg138; Ocean Drilling Program; ODP; Sample code/label; Sea surface temperature, annual mean; Sea surface temperature, annual mean, standard deviation; Sedimentation rate; South Pacific Ocean
Type:
Dataset
Format:
text/tab-separated-values, 3062 data points
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