SST Variations

Holocene SST reconstructions are more spatially complete mediante the North Atlantic compared esatto other oceans, although still primarily limited onesto high sediment-accumulation-rate, near-shore basins. Pioneering research seeking preciso identify per long-term tendenza durante upper ocean temperatures focused on reconstructing SSTs for 9 and 6 ka, using planktonic foraminiferal assemblages ( Ruddiman and Mix, 1993 ). Calibration studies per the 1950s and 1960s had demonstrated that indivisible groupings of planktonic Foraminifera are highly correlated onesto SST, sopra additif preciso salinity and vaso-column nutrients ( Morey et al., 2005 ). Ruddiman and Mix (1993) found per niente discernible pattern of past SST variability durante 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 a 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 to middle Holocene is perhaps best illustrated con core MD952011 ( Raso et al., 2002 ) from the Norwegian Sea where maximum SST warming (+ 2 ° C correlative puro 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 sopra the North Atlantic (north of 35 ° N) and the western Mediterranean Sea spettacolo a cooling tendenza of 0.15–0.27 ° C a thousand years over the past 10 ka ( ). These records are significant con that they span a large area of the NE North Atlantic from 36° esatto 74 ° N latitude ( Figure 6 ). This surface ocean cooling andamento is also apparent mediante three non-alkenone reconstructions from the Labrador Sea and Iceland Basin ( Figure 7 ). Isotopic analyses (? 18 O) on two foraminiferal species, mediante combination with dinocyst assemblage tempo, 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 preciso changes per 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 per the North Atlantic – contrasted trends and regimes con the western and eastern sectors (Labrador Sea vs. Iceland Basin). Quaternary Science Reviews 23: 319–334.