Export fluxes of calcite in the eastern equatorial Pacific from the Last Glacial Maximum to present

Abstract

[1] The eastern equatorial Pacific (EEP) is an important center of biological productivity, generating significant organic carbon and calcite fluxes to the deep ocean. We reconstructed paleocalcite flux for the past 30,000 years in four cores collected beneath the equatorial upwelling and the South Equatorial Current (SEC) by measuring ex 230 Th-normalized calcite accumulation rates corrected for dissolution with a newly developed proxy for ''fraction of calcite preserved.'' This method produced very similar results at the four sites and revealed that the export flux of calcite was 30-50% lower during the LGM compared to the Holocene. The internal consistency of these results supports our interpretation, which is also in agreement with emerging data indicating lower glacial productivity in the EEP, possibly as a result of lower nutrient supply from the southern ocean via the Equatorial Undercurrent. However, these findings contradict previous interpretations based on mass accumulation rates (MAR) of biogenic material in the sediment of the EEP, which have been taken as reflecting higher glacial productivity due to stronger wind-driven upwelling.

Timescales of lateral sediment transport in the Panama Basin as revealed by radiocarbon ages of alkenones, total organic carbon and foraminifera

“…The resuspended sediment is injected into the near-bottom water, where it is laterally displaced away from the topographical highs (Turnewitsch et al, 2008). This is in agreement with the 230 Th xs data from Kienast et al (2007), as the supplied material is likely to have been transported by bottom currents, according to the basic assumptions of the 230 Th normalization method (Francois et al, 2004). Based on modeling studies, Egbert et al contributed to the apparent sediment focusing, even though they were weaker than during the LGM .…”

“…Accumulation rates of sedimentary constituents related to marine productivity and vertical carbon export (e.g., organic carbon, calcium carbonate or barite) indicate higher glacial export rates compared to interglacials (Lyle et al, 2002;Paytan et al, 1996;Pedersen, 1983;Sarnthein et al, 1988), whereas proxies normalized to a "constant flux" proxy (i.e. 230 Thorium excess ) (Loubere, 1999;Loubere, 2000;Loubere et al, 2003;Loubere et al, 2004) and faunal assemblages (Loubere, 1999;Martinez et al, 2006) imply constant or reduced glacial productivity. The latter findings imply lateral particle transport and sediment focusing processes play an important role in this region.…”

“…The Panama Basin has been intensively studied for its climate and paleoproductivity history over glacial-interglacial timescales based on a wide range of proxies (Loubere, 1999;Loubere, 2000;Loubere et al, 2003;Loubere et al, 2004;Loubere and Richaud, 2007;Lyle et al, 2002;Lyle et al, 2005;Lyle et al, 2007;Martinez et al, 2006;Paytan et al, 1996;Pedersen, 1983;Pisias and Mix, 1997;Sarnthein et al, 1988). A conflict has emerged in terms of the past sedimentation dynamics of this region.…”

“…Using the 230 Thorium normalization method, several authors suggested that the sediment accumulation maxima observed in glacial sediments from the Panama Basin might be an artifact resulting from lateral supply rather than paleoproductivity Loubere et al, 2004;Marcantonio et al, 2001). Kienast et al (2007) report 230 Thorium excess ( 230 Th xs ) derived focusing factors (Ψ) for cores from the Panama Basin as high as Ψ=7.5, implying substantial contribution of laterally supplied sediment.…”

Opal burial in the equatorial Atlantic Ocean over the last 30 ka: Implications for glacial‐interglacial changes in the ocean silicon cycle

“…Conversely, the thermocline in the glacial eastern equatorial Pacific may have been deeper because of El Niño-like conditions there [Beaufort et al, 2001;Koutavas et al, 2002;Bradtmiller et al, 2006]. Evidence for a decreased N-S temperature gradient [Koutavas et al, 2002] and for decreased productivity in the EEP during the LGM [Beaufort et al, 2001;Loubere et al, 2004;Bradtmiller et al, 2006;Kienast et al, 2006b] suggests that upwelling was likely reduced at that time. If so, then this would have decreased nutrient supply to the Pacific surface ocean, suppressing productivity and resulting in lower glacial opal accumulation.…”