Can coral skeletal-bound nitrogen isotopes be used as a proxy for past bleaching?
- PDF / 3,465,281 Bytes
- 11 Pages / 547.087 x 737.008 pts Page_size
- 55 Downloads / 205 Views
(0123456789().,-volV) ( 01234567 89().,-volV)
Can coral skeletal-bound nitrogen isotopes be used as a proxy for past bleaching? Dirk V. Erler . Marı´a Salome´ Rangel . Alejandro Tagliafico . Jessica Riekenberg . Hanieh Tohidi Farid . Les Christidis . Sander R Scheffers . Janice M. Lough
Received: 7 November 2019 / Accepted: 4 October 2020 Ó Springer Nature Switzerland AG 2020
Abstract There is currently no reliable geochemical proxy of historical coral bleaching. Here we test the hypothesis that increases in the nitrogen isotopic signature of coral tissue, which is recorded in skeletalbound organic material (CS-d15N), can be used to detect coral bleaching events in the past. We measured CS-d15N in coral colonies that showed high density thermal stress bands associated with the 1998 and 2002 mass bleaching events on the central Great Barrier Reef. Analysis of coral cores from 2 inshore and 1 mid-shelf reef found that increases in CS-d15N occurred either side of the thermal stress events and were therefore unlikely to be a physiological response
Responsible Editor: J.C. Finlay. D. V. Erler (&) J. Riekenberg H. T. Farid Centre for Coastal Biogeochemistry, School of Environment Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia e-mail: [email protected] M. S. Rangel A. Tagliafico L. Christidis National Marine Science Centre, Southern Cross University, Coffs Harbour, NSW 2450, Australia S. R. Scheffers Marine Ecology Research Centre, School of Environment Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia J. M. Lough Australian Institute of Marine Science, Townsville, QLD 4810, Australia
to bleaching. We then assessed whether CS-d15N could be used to detect shelf-wide upwelling, which has been previously shown to coincide with mass bleaching events. For the inshore sites the response of CS-d15N to upwelling was not uniform between reefs or between colonies from the same reef. However, on the mid-shelf reef, increased CS-d15N during the known upwelling of 1998 was more consistent between cores. Analysis of a 23-year old coral core from the mid-shelf reef showed increased CS-d15N between 1983–1985 and 1997–2000, periods where strong El Nin˜o events were proceeded by intense wind-driven upwelling. We conclude that coral CSd15N is not a direct proxy for coral bleaching but can be used to detect prolonged and pervasive upwelling that coincides with mass bleaching events. Further validation with longer core records is required. Keywords Historical coral bleaching Nitrogen isotope Skeletal density Great Barrier Reef
Introduction The last four decades have been characterized by a seemingly unprecedented increase in the number of thermally-induced mass coral bleaching events throughout the world’s tropical oceans (Hughes et al. 2018a, b; Lough et al. 2018). For example, between 1979 and 1990 there were at least 60 thermal coral
123
Biogeochemistry
bleaching events recorded globally compared to just three between 1900 and 1980 (Glynn 1993). On
Data Loading...
