A study of the alkenone, TEX₈₆, and planktonic foraminifera in the Benguela Upwelling System: Implications for past sea surface temperature estimates

Abstract

[1] Suspended particulate matter from seawater and core top sediments were collected during 2003 Meteor cruise M57/1 in January-February from the continental margin off western South Africa for analysis of alkenones, glycerol dibiphytanyl glycerol tetraether (GDGT) lipids, and planktonic foraminifera. Alkenone analysis of suspended particulates in seawater and core top sediments indicates that U 37 K 0 temperatures were representative of annual mean sea surface temperature. In contrast, GDGT analysis suggests that TEX 86 temperatures are cold-biased due to upward transports of GDGTs produced below the mixed layer. The analysis of plankton tow samples revealed that the d 18 O of Globorotalia inflata in core top sediments could be biased toward lower temperatures due to subsurface calcification. Accordingly, our study shows that each paleotemperature proxy may record different temperature signals in the Benguela upwelling system emphasizing the general need to constrain potential biases in each proxy for better interpreting paleoclimate records.

Influence of ammonia oxidation rate on thaumarchaeal lipid composition and the TEX 86 temperature proxy

“…In contrast, cold TEX 86 temperatures are observed in surface sediments and SPM at high-nutrient/highproductivity sites such as upwelling systems (e.g., refs. [30][31][32][33].…”

“…Culture studies have shown that the average number of cyclopentyl moieties in GDGTs can increase with growth temperature in marine Archaea (19)(20)(21)(22); however, TEX 86 values of suspended particulate material (SPM) through the water column do not reflect in situ temperatures either in trend or in magnitude (23)(24)(25)(26)(27)(28)(29). TEX 86 -calculated temperatures in sinking particles and core-top sediments are often colder than mean annual average, especially in highly productive regions such as upwelling systems (30)(31)(32)(33). TEX 86 -calculated temperatures also often reach their maximum values below 200 m, and at these depths, TEX 86 can yield temperatures that are greater than local sea surface temperatures (23,26,28,34).…”

Alkenone and tetraether lipids reflect different seasonal seawater temperatures in the coastal northern South China Sea

“…Thaumarchaeota can also bloom during winter, thereby giving cold-biased TEX 86 temperature values, as observed in the North Sea . Other studies have shown that in some settings TEX 86 -based temperature values are lower than correspond ing U K 0 37 -based values, suggestive of a subsurface water signal recorded by TEX 86 , for example, in the Santa Barbara Basin (Huguet et al, 2007 ), the Benguela upwelling area (Lee et al, 2008 ) and the west coast of Africa (Lopes dos Santos et al, 2010 ). These results therefore highlight the importance of performi ng calibration studies using sediment traps and core tops before applying the temperat ure proxies in a given study area.…”

Spatial Variations in Archaeal Lipids of Surface Water and Core-Top Sediments in the South China Sea and Their Implications for Paleoclimate Studies

“…The reasons for the considerably lower TEX 86 temperatures in other parts of the SCS are unknown, and sampling in other seasons is needed to better understand temporal responses of archaeal abundances and community structure to changes in sea surface temperatures. Changes in nutrients (62), transportation of exogenous cold-water-sourced particles (35), or hydrodynamics of the water column (34,66) are possible reasons for the discrepancies between TEX 86 -derived sea surface temperatures and measured temperatures.…”