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Bates, NR, Amat A, Andersson AJ.  2010.  Feedbacks and responses of coral calcification on the Bermuda reef system to seasonal changes in biological processes and ocean acidification. Biogeosciences. 7:2509-2530.   10.5194/bg-7-2509-2010   AbstractWebsite

Despite the potential impact of ocean acidification on ecosystems such as coral reefs, surprisingly, there is very limited field data on the relationships between calcification and seawater carbonate chemistry. In this study, contemporaneous in situ datasets of seawater carbonate chemistry and calcification rates from the high-latitude coral reef of Bermuda over annual timescales provide a framework for investigating the present and future potential impact of rising carbon dioxide (CO(2)) levels and ocean acidification on coral reef ecosystems in their natural environment. A strong correlation was found between the in situ rates of calcification for the major framework building coral species Diploria labyrinthiformis and the seasonal variability of [CO(3)(2-)] and aragonite saturation state Omega(aragonite), rather than other environmental factors such as light and temperature. These field observations provide sufficient data to hypothesize that there is a seasonal 'Carbonate Chemistry Coral Reef Ecosystem Feedback' (CREF hypothesis) between the primary components of the reef ecosystem (i.e., scleractinian hard corals and macroalgae) and seawater carbonate chemistry. In early summer, strong net autotrophy from benthic components of the reef system enhance [CO(3)(2-)] and Omega(aragonite) conditions, and rates of coral calcification due to the photosynthetic uptake of CO(2). In late summer, rates of coral calcification are suppressed by release of CO(2) from reef metabolism during a period of strong net heterotrophy. It is likely that this seasonal CREF mechanism is present in other tropical reefs although attenuated compared to high-latitude reefs such as Bermuda. Due to lower annual mean surface seawater [CO(3)(2-)] and Omega(aragonite) in Bermuda compared to tropical regions, we anticipate that Bermuda corals will experience seasonal periods of zero net calcification within the next decade at [CO(3)(2-)] and Omega(aragonite) thresholds of similar to 184 mu moles kg(-1) and 2.65. However, net autotrophy of the reef during winter and spring (as part of the CREF hypothesis) may delay the onset of zero NEC or decalcification going forward by enhancing [CO(3)(2-)] and Omega(aragonite). The Bermuda coral reef is one of the first responders to the negative impacts of ocean acidification, and we estimate that calcification rates for D. labyrinthiformis have declined by > 50% compared to pre-industrial times.

Beman, JM, Chow CE, King AL, Feng YY, Fuhrman JA, Andersson A, Bates NR, Popp BN, Hutchins DA.  2011.  Global declines in oceanic nitrification rates as a consequence of ocean acidification. Proceedings of the National Academy of Sciences of the United States of America. 108:208-213.   10.1073/pnas.1011053108   AbstractWebsite

Ocean acidification produced by dissolution of anthropogenic carbon dioxide (CO2) emissions in seawater has profound consequences for marine ecology and biogeochemistry. The oceans have absorbed one-third of CO2 emissions over the past two centuries, altering ocean chemistry, reducing seawater pH, and affecting marine animals and phytoplankton in multiple ways. Microbially mediated ocean biogeochemical processes will be pivotal in determining how the earth system responds to global environmental change; however, how they may be altered by ocean acidification is largely unknown. We show here that microbial nitrification rates decreased in every instance when pH was experimentally reduced (by 0.05-0.14) at multiple locations in the Atlantic and Pacific Oceans. Nitrification is a central process in the nitrogen cycle that produces both the greenhouse gas nitrous oxide and oxidized forms of nitrogen used by phytoplankton and other microorganisms in the sea; at the Bermuda Atlantic Time Series and Hawaii Ocean Time-series sites, experimental acidification decreased ammonia oxidation rates by 38% and 36%. Ammonia oxidation rates were also strongly and inversely correlated with pH along a gradient produced in the oligotrophic Sargasso Sea (r(2) = 0.87, P < 0.05). Across all experiments, rates declined by 8-38% in low pH treatments, and the greatest absolute decrease occurred where rates were highest off the California coast. Collectively our results suggest that ocean acidification could reduce nitrification rates by 3-44% within the next few decades, affecting oceanic nitrous oxide production, reducing supplies of oxidized nitrogen in the upper layers of the ocean, and fundamentally altering nitrogen cycling in the sea.

Bresnahan, PJ, Wirth T, Martz TR, Andersson AJ, Cyronak T, D’Angelo S, Pennise J, Melville KW, Lenain L, Statom N.  2016.  A sensor package for mapping pH and oxygen from mobile platforms. Methods in Oceanography. 17:1-13.   10.1016/j.mio.2016.04.004   Abstract

A novel chemical sensor package named “WavepHOx” was developed in order to facilitate measurement of surface ocean pH, dissolved oxygen, and temperature from mobile platforms. The system comprises a Honeywell Durafet pH sensor, Aanderaa optode oxygen sensor, and chloride ion selective electrode, packaged into a hydrodynamic, lightweight housing. The WavepHOx has been deployed on a stand-up paddleboard and a Liquid Robotics Wave Glider in multiple near-shore settings in the Southern California Bight. Integration of the WavepHOx into these mobile platforms has enabled high spatiotemporal resolution pH and dissolved oxygen data collection. It is a particularly valuable tool for mapping shallow, fragile, or densely vegetated ecosystems which cannot be easily accessed by other platforms. Results from three surveys in San Diego, California, are reported. We show pH and dissolved oxygen variability >0.3 and >50% saturation, respectively, over tens to hundreds of meters to highlight the degree of natural spatial variability in these vegetated ecosystems. When deployed during an extensive discrete sampling program, the WavepHOx pH had a root mean squared error of 0.028 relative to pH calculated from fifty six measurements of total alkalinity and dissolved inorganic carbon, confirming its capacity for accurate, high spatiotemporal resolution data collection.