James GSST Variations
Holocene SST reconstructions are more spatially complete mediante the North Atlantic compared preciso other oceans, although still primarily limited to high sediment-accumulation-rate, near-shore basins. Pioneering research seeking esatto identify a long-term andamento mediante upper ocean temperatures focused on reconstructing SSTs for 9 and 6 ka, using planktonic foraminiferal assemblages ( Ruddiman and Mix, 1993 ). Calibration studies durante the 1950s and 1960s had demonstrated that insecable groupings of planktonic Foraminifera are highly correlated preciso SST, durante addenda preciso salinity and chicchera-column nutrients ( Morey et al., 2005 ). Ruddiman and Mix (1993) found giammai discernible pattern of past SST variability mediante the North Atlantic and questioned both the methodology used for quantitative reconstructions and the age control associated with variable sediment-accumulation rates.
Verso subsequent study of reconstructed summer SST for 6 ka, using verso variety of methods (diatom assemblages, marine mollusks, and dinoflagellate cysts), found that warmer conditions (+ 1–4 °C imparfaite preciso today) inundated the Norwegian Sea, Hudson Bay, Baffin Bay, Nares Strait, Davis Strait, Labrador Sea, and Greenland Sea during verso time when summertime insolation was approximately 7% higher than today ( Kerwin et al. (1999) , and references therein). This andamento of warmer-than-present SSTs during the early esatto middle Holocene is perhaps best illustrated durante core MD952011 ( Pelato et al., 2002 ) from the Norwegian Sea where maximum SST warming (+ 2 ° C relative puro today) accompanied the Holocene Thermal Maximum between 8.6 and 5.5 ka, followed by verso gradual cooling onesto today’s temperatures.
A major breakthrough in Holocene paleoceanography was made with the development of alkenone paleothermometry in the 1980s ( Brassell et al., 1986 ). Alkenones are long-chained ketones synthesized as membrane lipids by certain kinds of algae that are well preserved in marine sediments (see Alkenone Paleothermometry Based on the Haptophyte Algae ). The alkenone unsaturation index U K 37 is considered to be a robust proxy for SST because the algal organisms synthesizing alkenones must live in the photic zone, where their growth temperature is closely tied to SST. By measuring the alkenone unsaturation ratio preserved in a wide array of marine-sediment cores, a detailed picture of past surface ocean conditions ).
Alkenone-based SST reconstructions from seven high-accumulation sediment cores sopra the North Atlantic (north of 35 ° N) and the western Mediterranean Sea show a cooling andamento of 0.15–0.27 ° C per thousand years over the past 10 ka ( ). These records are significant per that they span per large distretto of the NE North Atlantic from 36° sicuro 74 ° N latitude ( Figure 6 ). This surface ocean cooling trend is also apparent per three non-alkenone reconstructions from the Labrador Sea and Iceland Basin ( Figure 7 ). Isotopic analyses (? 18 O) on two foraminiferal species, con combination with dinocyst assemblage scadenza, suggest that SSTs have been cooling steadily since the early Holocene ( Solignac et al., 2004 ). These ? 18 Oppure records each show more high-frequency variability than the alkenone-derived records, likely because of the sensitivity of isotopes to changes con sea-surface salinity as well as surface temperature ( Solignac et al., 2004 ).
PALEOCEANOGRAPHY, RECORDS | Postglacial North Atlantic
From ) Apparent long-term cooling of the sea surface per the northeast Atlantic and Mediterranean during the Holocene. Quaternary Science Reviews 21: 455–583.
From Solignac S, de Vernal A, and Hillaire-) Holocene sea-surface conditions mediante the North Atlantic – contrasted trends and regimes mediante the western and eastern sectors (Labrador Sea vs. Iceland Basin). Quaternary Science Reviews 23: tagliandi mixxxer 319–334.