High-resolution Mg/Ca ratios in a coralline red alga as a proxy for Bering Sea temperature variations from 1902-1967

• Published in: PALAIOS
• Main Authors: Hetzinger, Steffen, Halfar, Jochen, Kronz, Andreas, Steneck, Robert S., Adey, Walter, Lebednik, Phillip A., Schöne, Bernd R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: SEPM 2009
• Subjects: Amchitka; Amchitka Island; Bering Sea; Pacific; Subarctic; Aleutian Islands
• Online Access: https://oceanrep.geomar.de/id/eprint/9194/; https://oceanrep.geomar.de/id/eprint/9194/1/2009_Hetzinger_et_al._PALAIOS_MgCa-temp.pdf; http://palaios.geoscienceworld.org/; https://doi.org/10.2110/palo.2008.p08-116r

We present the first continuous, high-resolution record of Mg/Ca variations within an encrusting coralline red alga, Clathromorphum nereostratum, from Amchitka Island, Aleutian Islands. Mg/Ca ratios of individual growth increments were analyzed by measuring a singlepoint, electron-microprobe transect, yielding a resolution of ~15 samples/year and a 65-year record (1902–1967) of variations. Results show that Mg/Ca ratios in the high-Mg calcite algal framework display pronounced annual cyclicity and archive late spring–late fall sea-surface temperatures (SST) corresponding to the main season of algal growth. Mg/Ca values correlate well to local SST, as well as to an air temperature record from the same region. High spatial correlation to large-scale SST variability in the subarctic North Pacific is observed, with patterns of strongest correlation following the direction of major oceanographic features that play a key role in the exchange of water masses between the North Pacific and the Bering Sea. Our data correlate well with a shorter Mg/Ca record from ability of the alga to reliably record regional environmental signals. In addition, Mg/Ca ratios relate well to a 29-year δ18O time series measured on the same sample, providing additional support for the use of Mg in coralline red algae as a paleotemperature proxy that, unlike algal-δ18O, is not influenced by salinity fluctuations. Moreover, electron microprobe–based analysis enables higher sampling resolution and faster analysis, thus providing a promising approach for future studies of longer C. nereostratum records and applications to other coralline species.