Assessing the effect of dissolution on planktonic foraminiferal Mg/Ca ratios: Evidence from Caribbean core tops

Abstract

[1] In order to assess the dissolution effect on foraminiferal Mg/Ca ratios, we analyzed Mg/Ca of seven planktonic foraminiferal species and four of their varieties from Caribbean core tops from $900-4700 m water depth. Depending on the foraminiferal species and variety, Mg/Ca start to decline linearly below ], similar to decreases of $0.5-0.8 mmol/mol per kilometer below $2500-3000 m water depth. Above these speciesspecific critical levels, Mg/Ca remains stable with higher intraspecific Mg/Ca variability than below. We developed routines to correct Mg/Ca from below these critical thresholds for dissolution effects, which reduce the overall intraspecific variability by $24-64%, and provide dissolution-corrected Mg/Ca appropriate to calculate Holocene paleotemperatures. When taking into account only dissolutionunaffected Mg/Ca from <2000 m, the systematic succession of foraminiferal species according to their Mg/ Ca reflects expected calcification depths.

The centennial and millennial variability of the IndoPacific Warm Pool and the Indonesian Throughflow

“…In agreement with a previous study , and in contrast with another , our new core top data, in conjunction with data from other regions Dahl and Oppo, 2006;Ferguson et al, 2008;McConnell and Thunell, 2005;Mohtadi et al, 2011a;Regenberg et al, 2006], demonstrate that there is no discernable salinity influence on the Mg/Ca-based temperature estimates of G. ruber at low salinities. Arubszewski et al…”

Holocene and Eemian sea surface temperature trends as revealed by alkenone and Mg/Ca paleothermometry

“…Secondly, lateral transport through oceanic currents (Ohkouchi et al, 2002) or bioturbation (Bard, 2001) may have tended to smooth the SST signal regionally or downcore, respectively, two factors that are probably more effective for alkenones than for planktonic foraminifera. Thirdly, some intervals may have been affected by dissolution, one mechanism that artificially lowers the Mg/Ca (Regenberg et al, 2006). One easy way to check for the potential effect of dissolution resides in weighting the foraminifera prior to foraminifera cleaning, or eventually, measuring the sedimentary calcium carbonate content downcore.…”

Assessing the reliability of foraminiferal Mg/Ca thermometry by comparing field-samples and culture experiments: a review

“…The Dekens et al (2002) dis so lu tion cor rec tion was pre ferred in stead of that from Regenberg et al (2006) since the lat ter in cludes sam ples only from the Ca rib bean Sea, while the for mer in te grates over a wider area, in clud ing sam ples from the At lan tic and the Pa cific oceans. How ever, it is worth not ing that the Dekens et al (2002) dis so lution-cor rected cal i bra tion equa tions may not be the best in sit u ations where diagenesis ap pears to be the con trol ling dis so lu tion fac tor, rather than the [ ] D CO 3 2 -of bot tom wa ters.…”

“…All three can po ten tially act to off set the orig i nal geo chem is try of foraminiferal tests post-mor tem, ei ther in the wa ter col umn or at be neath the sea-floor (Pearson and Bur gess, 2008;Sadekov et al, 2010). Al though the for mer has been widely stud ied for the Mg/Ca palaeothermometer through wa ter depth transects, size-nor mal ized dis so lu tion prox ies, X-ray to mog ra phy and bulk sedimentological pa ram e ters (e.g., Lea et al, 2000Lea et al, , 2006Dekens et al, 2002;Rosenthal and Lohmann, 2002;Regenberg et al, 2006Regenberg et al, , 2014Fehrenbacher et al, 2006;Mekik et al, 2007;Huang et al, 2008;Mar tin, 2011, 2014;John stone et al, 2011), this is not the case for the other two. Recrystallisation (neomorphism), which re fers to the re place ment of pri mary by new crys tals of the same min eral (cal cite) spe cies (Folk, 1965), is of ten grad ual and very lo calized, which means that many rounds of dis so lu tion and re-precip i ta tion may be ap plied in or der for a new crys tal to be formed, and con se quently it is very dif fi cult to be traced in mod ern ma terial.…”