Variation in thickness of Globigerinoides ruber tests from the Scott Plateau, Timor Sea (6–60 ka)

A460

Goldschmidt Conference Abstracts 2006

Mg/Ca, stable isotopes and an important paleo-salintiy record from the indo-pacific warm pool

Variation in thickness of Globigerinoides ruber tests from the Scott Plateau, Timor Sea (6–60 ka)

B.N. OPDYKE1, J. EDWARDS1, H.C. BOSTOCK1, D.W. LEA2, H.J. SPERO3, M. GAGAN1, K. FIFIELD1

B.N. OPDYKE1, J.R. EDWARDS1, S. EGGINS2 1

1

Department of Earth and Marine Sciences, Research School of Earth Science, Research School of Physical Sciences and Engineering Australian National University, Australia ([email protected]; [email protected]; Helen. [email protected]; [email protected]; keith. fifi[email protected]) 2 Department of Geological Sciences and Marine Science Institute, UCSD, USA ([email protected]) 3 Department of Geology, UC Davis, USA (spero@geology. ucdavis.edu) Core MD-982167, latitude 13 8.86S, Longitude 121 34.69E, is located in the ideal location to monitor the changes in AustralAsian Mediterreanean Water as it flows from the Indonesian Archepelago. Recovered from 1981 m water depth, the core has a typical sedimentation rates of between 10 and 20 cm/ka, which has allowed us to recover a relatively high resolution paleoceanographic record. The Mg/Ca and d18O were run on Globigerinoides ruber (white variety) for the termination of the last Glacial cycle. We used a modified Lambeck and Chappell sea level curve to adjust for the ice volume signal (Lambeck and Chappell, 2001). The Mg/Ca signal was derived using the Lea et al.’s (2000) methods of preparation for planktonic foraminifera (Lea et al., 2000). The Mg/Ca signal was used as a proxy for temperature and subtracted from the residual d18O record to yield a Dd18O, which serves as a proxy for sea water salinity change. We found salinity freshened rapidly, by 0.7&, at 18,000 calendar years ago. The signal does is more saline between 13 and 10 ka, before freshening to 6 ka and then gradually becoming more saline to 2800 years ago. The mid-Holocene freshening of surface water corresponds to local strengthening of the Australian monsoon. The early, 18 ka, event is probably tracking an event farther a field.

References Lambeck, K., Chappell, J., 2001. Science 292, 679–686. Lea, D.W., Pak, D.K., Spero, H.J., 2000. Science 289, 1719–1724. doi:10.1016/j.gca.2006.06.926

Department of Earth and Marine Sciences, Australian National University, Australia ([email protected]; jonathan.edwards @ga.gov.au) 2 Research School of Earth Sciences, Australian National University, Australia ([email protected]) Chamber thickness of the near surface dwelling (0–50 m) planktonic foraminifera Globigerinoides ruber was measured from the Scott Plateau, Timor Sea spanning 6–63 ka. Chamber thickness was measured concurrently with Mg and Sr employing a novel approach; laser ablation inductively coupled mass spectrometer (LA-ICP-MS). This method allows for precise determination of depth profiles of trace elements and chamber thickness on individual foraminifera tests. Fifteen G. ruber per sample interval were analysed and the average value determined. During the Holocene average chamber thickness is 6.95 lm compared to an average of 8.62 lm for samples spanning the last glacial period through Stage 3 (18–63 ka). This represents a 20% decrease in chamber thickness during the Holocene compared to glacial to interstadial values. Comparison with the Vostok CO2atmospheric record (Shackelton, 2000)highlights a broad correlation with chamber thickness, where relatively thin chambers occur during periods of high CO2. It is proposed that this covariation is related to variations in the surface seawater carbonate ion concentration [CO3 2 ] through time.

Reference Shackelton, N.J., 2000. Science 289, 1897–1902. doi:10.1016/j.gca.2006.06.927