Carbon stable isotope record in the coral species Siderastrea stellata: A link to the Suess Effect in the tropical South Atlantic Ocean

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Coral skeletons are natural archives whose geochemical signatures provide insights into the tropical ocean history beyond the instrumental record. Carbon stable isotopes from coral skeletons (δ13Ccoral) have been used as a proxy for multiple variables on a seasonal basis. Long-term changes in coral δ13C could be related to the changing isotopic composition of the dissolved inorganic carbon (δ13CDIC). δ13CDIC in turn reflects changes in the δ13C of atmospheric CO2, which in the modern Earth system is governed primarily by anthropogenic injection of CO2 into the atmosphere – a process known as the Suess Effect. Here we report three δ13C coral-based records of Siderastrea stellata from the tropical South Atlantic. U-series dating for the colonies 12SFB-1, 13SS-1 and 13SS-2 suggests these corals lived 13, 57 and 65 years, respectively. Short-term δ13C variations in their skeletal aragonite are dominated by interannual variation. All three δ13C records additionally exhibit an overall decreasing trend, with a depletion of about −0.0243 ± 0.0057‰·yr−1 (12SFB-1), −0.0208 ± 0.0007‰·yr−1 (13SS-1) and −0.0214 ± 0.0013‰·yr−1 (13SS-2). These rates of the coral records from Rocas Atoll are similar to the reported trend for the δ13C of atmospheric CO2 over the years 1960–1990 (−0.023 to −0.029‰·yr−1), and to the decreasing rates of global δ13CDIC. Our findings suggest that multiple δ13C coral-based records are required for confidently identifying local changes in the δ13CDIC of the ocean. This information, in turn, can be used to infer changes in the δ13C of the atmospheric CO2 composition and provide valuable information about recent changes on the carbon biogeochemical cycle during the Anthropocene epoch.NSP acknowledges the National Counsel of Technological and Scientific Development (CNPq) for a Post-Doctoral Scholarship Proc. no 150405/2015-4. We thank the chief of the Biological Reserve of Rocas Atoll, Maurizélia de Brito Silva and the field team Tiago Albuquerque, Miguel Miranda, Mirella B. Costa and Eduardo Macêdo, for the great assistance in this study. We thank Gilsa Santana, Vilma Sobral (NEG-LABISE, Brazil) and Bo Petersen (University of Copenhagen) for assisting in stable isotope measurements. We are thankful for the critical and constructive comments of the anonymous reviewers. The 2013 field work was partially supported by National Geographic Waitt Foundation grant W21-12 to K.H.K. and R.K.P.K. U-Th dating was supported by grants from Ministry of Science and Technology (MOST) (105-2119-M-002-001, 106-2628-M-002-013 to C.-C.S.) and the National Taiwan University (105R7625 to C.-C.S.). This manuscript is the scientific contribution no 288 of the NEG-LABISE, UFPE, a contribution of the Reef Ecosystems Working Group of the INCT Ambientes Marinhos Tropicais (InctAmbTropic – CNPq #565.054/2010-4) and represents contribution 5470 of the University of Maryland Center for Environmental Science

Photobiology of corals from Brazil\u27s near-shore marginal reefs of Abrolhos

Coral communities were examined from highly turbid near-shore marginal reefs of Abrolhos (Brazil) to test a paradigm previously developed from observations in clear water reefs; specifically, that coral photobiological properties follow a highly conserved linear relationship with optical depth (ζ) via preferential 'non-photochemical' over 'photochemical' dissipation of absorbed light energy. PAM flourometry in situ was used to examine the photobiology of the most dominant coral species throughout the platform surfaces and bases of Abrolhos' characteristic 'chapeirões' reef framework; however, none of the species consistently adhered to the 'clear water paradigm'. PAM measurements further demonstrated that species conformed to two different strategies of non-photochemical energy dissipation: transient but relatively rapid for the two closely related endemic species (Mussismilia braziliensis and Mussismilia harttii) as opposed to more persistent for Montastrea cavernosa, Porites astreoides and Siderastrea stellata. Further experiments demonstrated that tolerance to anomalous stress amongst species did not correspond with the non-photochemical energy dissipation strategy present but was consistent with the relative dominance of species within the chapeirões coral communities. © 2012 Springer-Verlag

The construction of causal networks to estimate coral bleaching intensity

Current metrics for predicting bleaching episodes, e.g. NOAA's Coral Reef Watch Program, do not seem to apply well to Brazil's marginal reefs located in Bahia state and alternative predictive approaches must be sought for effective long term management. Bleaching occurrences at Abrolhos have been observed since the 1990s but with a much lower frequency/extent than for other reef systems worldwide. We constructed a Bayesian Belief Network (BN) to back-predict the intensity of bleaching events and learn how local and regional scale forcing factors interact to enhance or alleviate coral bleaching specific to Abrolhos. Bleaching intensity data were collected for several reef sites across Bahia state coast (~12°-20°S; 37°-40°W) during the austral summer 1994-2005 and compared to environmental data: sea surface temperature (SST), diffuse light attenuation coefficient at 490 nm (K490), rain precipitation, wind velocities, and El Niño Southern Oscillation (ENSO) proxies. Conditional independence tests were calculated to produce four specialized BNs, each with specific factors that likely regulate bleaching intensity. All specialized BNs identified that a five-day accumulated SST proxy (SSTAc5d) was the exclusive parent node for coral bleaching producing a total predictive rate of 88% based on SSTAc5d state. When SSTAc5d was simulated as unknown, the Thermal-Eolic Resultant BN kept the total predictive rate of 88%. Our approach has produced initial means to predict beaching intensity at Abrolhos. However, the robustness of the model required for management purposes must be further (and regularly) operationally tested with new in situ and remote sensing data. © 2013 Elsevier Ltd

Mid to late 20th century freshening of the western tropical South Atlantic triggered by southward migration of the Intertropical Convergence Zone

In the tropical Atlantic Ocean, the Intertropical Convergence Zone (ITCZ) is an important climate feature controlled by the interhemispheric sea surface temperature (SST) gradient, and greatly influences rainfall patterns over the adjacent continents. To better understand ITCZ dynamics in the context of past and future climate change, long-term oceanic records are needed, but observational data are limited in temporal extent. Shallow-water corals provide seasonally-resolved archives of climate variability over the tropical ocean. Here we present seasonally-resolved records of stable oxygen (δ18O) and carbon (δ13C) isotope values of a Siderastrea stellata coral from northeastern Brazil (Maracajaú, ~5°S). We show that the long-term trends in the record of coral δ18O values are not primarily driven by SST but by hydrological changes at the sea surface. Combining the record of coral δ18O values with instrumental SST, we present the first reconstruction of seawater δ18O changes (δ18Oseawater) in the western tropical South Atlantic back to the early 20th century, a parameter that is related to changes in sea surface salinity. The reconstructed δ18Oseawater changes indicate a prominent freshening between the mid-1940's and mid-1970's, which coincides with a weakening of the Atlantic interhemispheric SST gradient during this time interval. Our results suggest that the weakened Atlantic SST gradient resulted in a southward shift of the thermal equator that was accompanied by a southward migration of the ITCZ, resulting in freshening of the western tropical South Atlantic during the mid to late 20th century

Roundtable Discussion Groups Summary Papers: Environmental Bio-Indicators in Coral Reef Ecosystems: the Need to Align Research, Monitoring, and Environmental Regulation

Editors\u27 Note: At the 14th International Conference on Environmental Bioindicators (14th ICEBI) held in Linthicum Heights, Maryland, USA on 24–26 April 2006, the Conference Chairs and Program Committee initiated the Roundtable Discussion Groups as a regular feature of this and future conferences. The Discussions are designed to generate focused debate around key topic areas, led by academic, government and industry experts, and are structured to produce definitive papers for peer review and publication in EBI\u27s first-quarter issue of each publication year, albeit this year the papers will be published over the first two issues of 2007. The three Roundtables of the 14th ICEBI posed questions revolving around the chosen topic areas of Mercury Bioindicators, Marine Ecosystem-level Indicators, and Regulatory and Policy Uses of Bioindicators, and moved from “what we know” to “where we need to go” and “what are the policy implications from our discussions and conclusions.” The following paper on coral reef indicators is the first product of this undertaking. The second Roundtable paper on Mercury Bioindicators, along with a summary of the third Roundtable on Regulatory and Policy Uses of Bioindicators, will occur in our next issue. A roundtable workshop was held on 24–26 April 2006 at the 14th International Conference on Environmental Bioindicators (14th ICEBI) to discuss environmental bioindicators as they apply to the coral reefs. Participants discussed procedures and potential bioindicators currently being used to monitor these ecosystems, those showing promise for future use, and candidates for future research and development. Attendees represented research and educational institutions, environmental consulting firms, and US federal government regulatory agencies. Despite the fact that these three interest-groups have similar ultimate objectives of protecting coral reef ecosystems, they are engaged in different activities, using different jargon and techniques, and are pursuing different proximal objectives. Their different perspectives presented challenges for information transfer among the groups. Coral reef scientists, both descriptive and experimental, are attempting to explain the underlying processes controlling reef health, and assign functional relationships within that system, making it possible to predict effects of natural or anthropogenic perturbations. Individuals involved in monitoring are attempting to document components of the ecosystem and their characters that might indicate the state of reef health through time, generally at the macro-scale. Such monitoring generally utilizes at least some of the basic ecological, geological, chemical, or physical relationships defined by the first group. The third group – the environmental regulators and resource managers – is attempting to set limits for defining methods that will defensively document transgressions by parties causing damage to the environment. They also provide guidance for remediation. Management objectives almost universally require “reference points” or “bands” or standards against which alleged violations can be compared and which can be confidently and demonstrably traced to some anthropogenic source, within the guidelines of the law. One of the problems recognized in the workshop was that differences in their respective objectives created communication and information gaps. Each group is encouraged to become conversant with the terminology and objectives of the other groups to provide a legal framework to effect environmental protection. Thus, for research and monitoring groups, reviewing the effectiveness of one bioindicator over another for predicting anthropogenic effects, although important, may be premature. Rather, it is more important to first understand the ultimate requirements of local, state, and federal governments, understand the staff and funding limitations of the resource management agencies, and become conversant with resource management terminology and needs. Then specific and relevant information can be channeled to the responsible regulatory bodies that will assist in achieving the common ultimate goal of environmental protection of coral reefs. A clear conclusion from this workshop is that a bioindicator review process must “start with the end in mind.