Location map of seven sediment cores from the North Atlantic and western Mediterranean Sea

Location map of seven sediment cores from the North Atlantic and western Mediterranean Sea

SST Variations

Holocene SST reconstructions are more spatially complete mediante the North Atlantic compared esatto other oceans, although still primarily limited esatto high sediment-accumulation-rate, near-shore basins. Pioneering research seeking preciso identify a long-term andamento durante upper ocean temperatures focused on reconstructing SSTs for 9 and 6 ka, using planktonic foraminiferal assemblages ( Ruddiman and Mix, 1993 ). Calibration studies mediante the 1950s and 1960s had demonstrated that indivis groupings of planktonic Foraminifera are highly correlated preciso SST, durante addition sicuro salinity and chicchera-column nutrients ( Morey et al., 2005 ). Ruddiman and Mix (1993) found niente affatto discernible pattern of past SST variability sopra 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 a 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 a time when summertime insolation was approximately 7% higher than today ( Kerwin et al. (1999) , and references therein). This movimento of warmer-than-present SSTs during the early to middle Holocene is perhaps best illustrated per core MD952011 ( Pelato et al., 2002 ) from the Norwegian Sea where maximum SST warming (+ 2 ° Codice sconto muddy matches C relative esatto today) accompanied the Holocene Thermal Maximum between 8.6 and 5.5 ka, followed by per gradual cooling to 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 mediante the North Atlantic (north of 35 ° N) and the western Mediterranean Sea esibizione a cooling movimento of 0.15–0.27 ° C per thousand years over the past 10 ka ( ). These records are significant in that they span verso large dipartimento of the NE North Atlantic from 36° sicuro 74 ° N latitude ( Figure 6 ). This surface ocean cooling tendenza is also apparent in three non-alkenone reconstructions from the Labrador Sea and Iceland Basin ( Figure 7 ). Isotopic analyses (? 18 Oppure) on two foraminiferal species, sopra combination with dinocyst assemblage data, suggest that SSTs have been cooling steadily since the early Holocene ( Solignac et al., 2004 ). These ? 18 O records each show more high-frequency variability than the alkenone-derived records, likely because of the sensitivity of isotopes puro changes in 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 durante 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 in the North Atlantic – contrasted trends and regimes sopra the western and eastern sectors (Labrador Sea vs. Iceland Basin). Quaternary Science Reviews 23: 319–334.

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