Location map of seven sediment cores from the North Atlantic and western Mediterranean Sea
SST Variations
Holocene SST reconstructions are more spatially complete con the North Atlantic compared onesto other oceans, although still primarily limited preciso high sediment-accumulation-rate, near-shore basins. Pioneering research seeking puro identify verso long-term andamento sopra 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 excretion groupings of planktonic Foraminifera are highly correlated onesto SST, per accessit preciso salinity and vaso-column nutrients ( Morey et al., 2005 ). Ruddiman and Mix (1993) found per niente discernible pattern of past SST variability in the North Atlantic and questioned both the methodology used for quantitative reconstructions and the age control associated with variable sediment-accumulation rates.
Per subsequent study of reconstructed summer SST for 6 ka, using per variety of methods (diatom assemblages, marine mollusks, and dinoflagellate cysts), found that warmer conditions (+ 1–4 °C incomplete onesto 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 inclinazione of warmer-than-present SSTs during the early esatto middle Holocene is perhaps best illustrated mediante core MD952011 ( Raso et al., 2002 ) from the Norwegian Sea where maximum SST warming (+ 2 ° C incomplete sicuro today) accompanied the Holocene Thermal Maximum between 8.6 and 5.5 ka, followed by militarycupid sito di incontri 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 con the North Atlantic (north of 35 ° N) and the western Mediterranean Sea show a cooling trend of 0.15–0.27 ° C verso thousand years over the past 10 ka ( ). These records are significant mediante that they span verso large sezione of the NE North Atlantic from 36° puro 74 ° N latitude ( Figure 6 ). This surface ocean cooling tendenza is also apparent mediante three non-alkenone reconstructions from the Labrador Sea and Iceland Basin ( Figure 7 ). Isotopic analyses (? 18 Oppure) on two foraminiferal species, durante combination with dinocyst assemblage datazione, suggest that SSTs have been cooling steadily since the early Holocene ( Solignac et al., 2004 ). These ? 18 Ovvero records each show more high-frequency variability than the alkenone-derived records, likely because of the sensitivity of isotopes sicuro 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 sopra the northeast Atlantic and Mediterranean during the Holocene. Quaternary Science Reviews 21: 455–583.
From Solignac S, de Vernal Per, and Hillaire-) Holocene sea-surface conditions per the North Atlantic – contrasted trends and regimes mediante the western and eastern sectors (Labrador Sea vs. Iceland Basin). Quaternary Science Reviews 23: 319–334.