Phasing of deglacial warming and Laurentide Ice Sheet meltwater in the Gulf of Mexico

Abstract

Evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation. However, existing studies show that deglacial warming was asynchronous across the tropical band, complicating the identification of causal mechanisms. The Orca Basin in the northern Gulf of Mexico is ideally located to record subtropical Atlantic sea-surface temperature (SST) warming in relation to meltwater input from the Laurentide Ice Sheet. Paired ␦ 18 O and Mg/Ca data on the planktonic foraminifer Globigerinoides ruber from core EN32-PC6 are used to separate deglacial changes in SST and ␦ 18 O of seawater. SST as calculated from Mg/Ca data increased by Ͼ3 ؇C from ca. 17.2 to 15.5 ka in association with Heinrich event 1 and was not in phase with Greenland air temperature. Subtracting temperature effects from ␦ 18 O values in G. ruber reveals two excursions representing Laurentide meltwater input to the Gulf of Mexico, one of Ͼ1.5‰ from ca. 16.1 to 15.6 ka and a second major spike of Ͼ2.5‰ from ca. 15.2 to 13.0 ka that encompassed meltwater pulse 1A and peaked ca. 13.8 ka during the Bølling-Å llerød. Conversion to salinity through the use of a Laurentide meltwater end member of ؊25‰ indicates that near-surface salinity decreased by 2‰-4‰ during these spikes. These results suggest that Gulf of Mexico SST warming preceded peak Laurentide Ice Sheet decay and the Bølling-Å llerød interval by Ͼ2 k.y. and that heat was retained in the subtropical Atlantic during Heinrich event 1, consistent with modulation of deglacial climate by thermohaline circulation.

Hydrology and climatology at Laguna La Gaiba, lowland Bolivia: complex responses to climatic forcings over the last 25 000 years

“…The two stage nature of change across the YD interval indicated here is also of interest. A similar structure to the YD has been reported elsewhere including Lea et al (2003) from the Cariaco Basin; Sifeddine et al (2003) from Lake Caçó, Brazil; Flower et al (2004) from the Gulf of Mexico and Rein et al (2005) based on a marine record from coastal Peru. Unfortunately, integrating these patterns (warmer/cooler, wetter/drier) in terms of coherent climatologies seems impossible at this stage.…”

Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

“…5bee; and 11 ka that were consistent with a depleted meltwater signal (Kennett and Shackleton, 1975;Leventer et al, 1982) and characteristic low-salinity foraminiferal assemblages during the deglaciation (Kennett et al, 1985). Other records with more precise age control have demonstrated variations in the volume of LIS meltwater delivered to the Gulf of Mexico (Flower et al, 2004), with rapid and high frequency shifts in surface water d 18 O sw on decadal timescales (Williams et al, 2012). All support the variable influence of LIS meltwater in the Gulf of Mexico during the last deglaciation (Flower et al, 2011).…”

“…Laboratory culture experiments with live O. universa grown under low light produced the empirical calibration (Bemis et al, 1998): (Lea et al, 1999;Russell et al, 2004), with confirmation from sediment trap studies (Anand et al, 2003). Here we use the Mg/Ca-temperature relationship of Russell et al (2004) (Flower et al, 2004;Hill et al, 2006;Hoffman et al, 2012;Lea et al, 2000;Obbink et al, 2010;Schmidt et al, 2004;Williams et al, 2012).…”

“…Oxygen isotope analyses of marine sedimentary records proximal to LIS meltwater outflow offer the most direct evidence of the isotopic evolution of the LIS, and help to constrain the location and timing of routing of meltwater (e.g., Aharon, 2003Aharon, , 2006Broecker et al, 1989;Carlson, 2009;Carlson et al, 2007;Flower et al, 2004;Hill et al, 2006;Hoffman et al, 2012;Keigwin et al, 1991;Williams et al, 2012). However, mixing models of meltwater contributions to the ocean typically assume a constant d 18 O w value for the LIS (À25 or À35‰; Aharon, 2006;Carlson, 2009;Carlson et al, 2007;Hill et al, 2006;Obbink et al, 2010), and do not attempt to incorporate the complex spatial heterogeneity in d 18 O w observed in modern continental ice sheets (Masson-Delmotte et al, 2008;Vinther et al, 2009).…”

“…Foraminifer d 18 Ο c records from multiple shells in a single sample provide a qualitative measure of the geochemistry of Mississippi River input into the Gulf of Mexico, which is observed as a large decrease in shell d 18 Ο c . Studies have used these data to estimate the d 18 Ο w of a freshwater endmember in meltwater runoff (Flower et al, 2004;Hill et al, 2006;Williams et al, 2012) using simple mixing models. However, using these previously collected data sets, one cannot directly compute meltwater d 18 O w without a priori knowledge or assumptions about average seawater d 18 O sw and salinity over the coring site.…”