HR: 0800h
AN: PP31B-0425    [Abstracts]
TI: Evidence of Sr/Ca and Mg/Ca Temperature Invariance in Live Aragonitic Hoeglundina elegans Tests from the Little Bahama Bank
AU: * Blanks, J K
EM: jkblank@mailbox.sc.edu
AF: Dept. of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, 921 Assembly Street, Lexington, SC 29208, United States
AU: Hintz, C J
EM: chris.hintz@msci.sc.edu
AF: Dept. of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, 921 Assembly Street, Lexington, SC 29208, United States
AU: Chandler, G T
EM: tchandler@sc.edu
AF: Dept. of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, 921 Assembly Street, Lexington, SC 29208, United States
AU: Shaw, T J
EM: shaw@chem.sc.edu
AF: Dept. of Chemistry and Biochemistry, University of South Carolina, S. Main Street, Columbia, SC 29208, United States
AU: McCorkle, D C
EM: dmccorkle@whoi.edu
AF: Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, United States
AU: Bernhard, J M
EM: jbernhard@whoi.edu
AF: Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, United States
AB: Mg/Ca and Sr/Ca were analyzed from core-top individual Hoeglundina elegans aragonitic tests collected from three continental slope depths within the South Carolina and Little Bahama Bank continental slope environs (220 m to 1084 m). Our study utilized only individuals that labeled with the vital probe CellTracker Green – unlike bulk core-top material often stained with Rose Bengal, which has known inconsistencies in distinguishing live from dead foraminifera. DSr x 10 values were consistently 1.74 $ pm 0.23 across all sampling depths. The analytical error in DSr values (0.7%) determined by ICP-MS between repeated measurements on individual H. elegans tests across all depths was less than analytical error on repeated measurements from standards. Variation in DSr values was not directly explained by a linear temperature relationship (p=0.0003, R²=0.44) over the temperature range of 4.9-11.4°C with a sensitivity of 59.8 μmol/mol/1°C. The standard error by regressing DSr across temperature yields + 3.4°C, which is nearly 3x greater that reported in previous studies. Sr/Ca was more sensitive for calibrating temperature than Mg/Ca in H. elegans. Observed scatter in DSr was too great across individuals of the same size and of different sizes to resolve ontogenetic effects. However, higher DSr values were associated with smaller individuals and warmer/shallower sampling depths. The highest DSr values were observed at the intermediate sampling depth (~600 m). No significant ontogenetic relationship was found across DSr values in different sized individuals due to tighter overall constrained variance; however lower DSr values were observed from several smaller individuals. Several dead tests of H. elegans showed no significant differences in DSr values compared to live specimens cleaned by standard cleaning methods, unlike higher dead than live DMg values observed for the same individuals. There were no significant deviations in DSr across batches cleaned on separate days, unlike the observed sensitivity of DMg across batches. A subset of samples were reductively cleaned (hydrazine solution); and exhibited DMg values within analytical precision of those observed for non-reductively cleaned samples. Therefore, deviations in DMg values resulting from the removal of the reductive cleaning step did not explain analytical errors greater than published values for Mg/Ca or the high variance across same sized individuals. Variation in DMg values across the same cleaning methods and from dead individuals suggests the need for a careful look into how foraminiferal aragonite should be processed. These findings provide evidence that both Mg and Sr in benthic foraminiferal aragonite reflect factors in addition to temperature and pressure that may interfere with absolute temperature calibrations. Funded by NSF OCE 0351029, OCE 0437366, and OCE-0350794.
DE: 0419 Biomineralization
DE: 0424 Biosignatures and proxies
DE: 3030 Micropaleontology (0459, 4944)
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL (0460)
DE: 4875 Trace elements (0489)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting