SST Variations
Holocene SST reconstructions are more spatially complete mediante the North Atlantic compared preciso other oceans, although still primarily limited puro high sediment-accumulation-rate, near-shore basins. Pioneering research seeking onesto identify per long-term andamento per upper ocean temperatures focused on reconstructing SSTs for 9 and 6 ka, using nudistfriends planktonic foraminiferal assemblages ( Ruddiman and Mix, 1993 ). Calibration studies sopra the 1950s and 1960s had demonstrated that un groupings of planktonic Foraminifera are highly correlated to SST, con accessit preciso salinity and water-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 verso variety of methods (diatom assemblages, marine mollusks, and dinoflagellate cysts), found that warmer conditions (+ 1–4 °C divisee 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 andamento of warmer-than-present SSTs during the early onesto middle Holocene is perhaps best illustrated in core MD952011 ( Calvo et al., 2002 ) from the Norwegian Sea where maximum SST warming (+ 2 ° C imparfaite esatto today) accompanied the Holocene Thermal Maximum between 8.6 and 5.5 ka, followed by per 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 mediante the North Atlantic (north of 35 ° N) and the western Mediterranean Sea spettacolo a cooling andamento of 0.15–0.27 ° C a thousand years over the past 10 ka ( ). These records are significant durante that they span per large dipartimento of the NE North Atlantic from 36° esatto 74 ° N latitude ( Figure 6 ). This surface ocean cooling tendenza is also apparent con three non-alkenone reconstructions from the Labrador Sea and Iceland Basin ( Figure 7 ). Isotopic analyses (? 18 Ovverosia) on two foraminiferal species, mediante combination with dinocyst assemblage momento, suggest that SSTs have been cooling steadily since the early Holocene ( Solignac et al., 2004 ). These ? 18 Ovverosia records each show more high-frequency variability than the alkenone-derived records, likely because of the sensitivity of isotopes to changes durante 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 con 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 mediante the North Atlantic – contrasted trends and regimes sopra the western and eastern sectors (Labrador Sea vs. Iceland Basin). Quaternary Science Reviews 23: 319–334.
