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Regnier, P, Friedlingstein P, Ciais P, Mackenzie FT, Gruber N, Janssens IA, Laruelle GG, Lauerwald R, Luyssaert S, Andersson AJ, Arndt S, Arnosti C, Borges AV, Dale AW, Gallego-Sala A, Godderis Y, Goossens N, Hartmann J, Heinze C, Ilyina T, Joos F, LaRowe DE, Leifeld J, Meysman FJR, Munhoven G, Raymond PA, Spahni R, Suntharalingam P, Thullner M.  2013.  Anthropogenic perturbation of the carbon fluxes from land to ocean. Nature Geoscience. 6:597-607.   10.1038/ngeo1830   AbstractWebsite

A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean. So far, global carbon budget estimates have implicitly assumed that the transformation and lateral transport of carbon along this aquatic continuum has remained unchanged since pre-industrial times. A synthesis of published work reveals the magnitude of present-day lateral carbon fluxes from land to ocean, and the extent to which human activities have altered these fluxes. We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr(-1) since pre-industrial times, mainly owing to enhanced carbon export from soils. Most of this additional carbon input to upstream rivers is either emitted back to the atmosphere as carbon dioxide (similar to 0.4 Pg C yr(-1)) or sequestered in sediments (similar to 0.5 Pg C yr(-1)) along the continuum of freshwater bodies, estuaries and coastal waters, leaving only a perturbation carbon input of similar to 0.1 Pg C yr(-1) to the open ocean. According to our analysis, terrestrial ecosystems store similar to 0.9 Pg C yr(-1) at present, which is in agreement with results from forest inventories but significantly differs from the figure of 1.5 Pg C yr(-1) previously estimated when ignoring changes in lateral carbon fluxes. We suggest that carbon fluxes along the land-ocean aquatic continuum need to be included in global carbon dioxide budgets.

Sutton, AJ, Feely RA, Maenner-Jones S, Musielwicz S, Osborne J, Dietrich C, Monacci N, Cross J, Bott R, Kozyr A, Andersson AJ, Bates NR, Cai WJ, Cronin MF, DeCarlo EH, Hales B, Howden SD, Lee CM, Manzello DP, McPhaden MJ, Melendez M, Mickett JB, Newton JA, Noakes SE, Noh JH, Olafsdottir SR, Salisbury JE, Send U, Trull TW, Vandemark DC, Weller RA.  2019.  Autonomous seawater pCO(2) and pH time series from 40 surface buoys and the emergence of anthropogenic trends. Earth System Science Data. 11:421-439.   10.5194/essd-11-421-2019   AbstractWebsite

Ship-based time series, some now approaching over 3 decades long, are critical climate records that have dramatically improved our ability to characterize natural and anthropogenic drivers of ocean carbon dioxide (CO2) uptake and biogeochemical processes. Advancements in autonomous marine carbon sensors and technologies over the last 2 decades have led to the expansion of observations at fixed time series sites, thereby improving the capability of characterizing sub-seasonal variability in the ocean. Here, we present a data product of 40 individual autonomous moored surface ocean pCO(2) (partial pressure of CO2) time series established between 2004 and 2013, 17 also include autonomous pH measurements. These time series characterize a wide range of surface ocean carbonate conditions in different oceanic (17 sites), coastal (13 sites), and coral reef (10 sites) regimes. A time of trend emergence (ToE) methodology applied to the time series that exhibit well-constrained daily to interannual variability and an estimate of decadal variability indicates that the length of sustained observations necessary to detect statistically significant anthropogenic trends varies by marine environment. The ToE estimates for seawater pCO(2) and pH range from 8 to 15 years at the open ocean sites, 16 to 41 years at the coastal sites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO(2) time series, Woods Hole Oceanographic Institution Hawaii Ocean Time-series Station (WHOTS) in the subtropical North Pacific and Stratus in the South Pacific gyre, have been deployed longer than the estimated trend detection time and, for these, deseasoned monthly means show estimated anthropogenic trends of 1.9 +/- 0.3 and 1.6 +/- 0.3 mu atm yr(-1), respectively. In the future, it is possible that updates to this product will allow for the estimation of anthropogenic trends at more sites; however, the product currently provides a valuable tool in an accessible format for evaluating climatology and natural variability of surface ocean carbonate chemistry in a variety of regions. Data are available at https.//doi. org/10.7289/V5DB8043 and https.//www.nodc.noaa.gov/ocads/oceans/Moorings/ndp097.html (Sutton et al., 2018).

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Lebrato, M, Andersson AJ, Ries JB, Aronson RB, Lamare MD, Koeve W, Oschlies A, Iglesias-Rodriguez MD, Thatje S, Amsler M, Vos SC, Jones DOB, Ruhl HA, Gates AR, McClintock JB.  2016.  Benthic marine calcifiers coexist with CaCO3-undersaturated seawater worldwide. Global Biogeochemical Cycles. 30:1038-1053.   10.1002/2015GB005260   Abstract

Ocean acidification and decreasing seawater saturation state with respect to calcium carbonate (CaCO3) minerals have raised concerns about the consequences to marine organisms that build CaCO3 structures. A large proportion of benthic marine calcifiers incorporate Mg2+ into their skeletons (Mg-calcite), which, in general, reduces mineral stability. The relative vulnerability of some marine calcifiers to ocean acidification appears linked to the relative solubility of their shell or skeletal mineralogy, although some organisms have sophisticated mechanisms for constructing and maintaining their CaCO3 structures causing deviation from this dependence. Nevertheless, few studies consider seawater saturation state with respect to the actual Mg-calcite mineralogy (ΩMg-x) of a species when evaluating the effect of ocean acidification on that species. Here, a global dataset of skeletal mole % MgCO3 of benthic calcifiers and in situ environmental conditions spanning a depth range of 0 m (subtidal/neritic) to 5600 m (abyssal) was assembled to calculate in situ ΩMg-x. This analysis shows that 24% of the studied benthic calcifiers currently experience seawater mineral undersaturation (ΩMg-x < 1). As a result of ongoing anthropogenic ocean acidification over the next 200 to 3000 years, the predicted decrease in seawater mineral saturation will expose approximately 57% of all studied benthic calcifying species to seawater undersaturation. These observations reveal a surprisingly high proportion of benthic marine calcifiers exposed to seawater that is undersaturated with respect to their skeletal mineralogy, underscoring the importance of using species-specific seawater mineral saturation states when investigating the impact of CO2-induced ocean acidification on benthic marine calcification.

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Marshall, J, Andersson A, Bates N, Dewar W, Doney S, Edson J, Ferrari R, Forget G, Fratantoni D, Gregg M, Joyce T, Kelly K, Lozier S, Lumpkin R, Maze G, Palter J, Samelson R, Silverthorne K, Skyllingstad E, Straneo F, Talley L, Thomas L, Toole J, Weller R, Climode G.  2009.  The CLIMODE FIELD CAMPAIGN Observing the Cycle of Convection and Restratification over the Gulf Stream. Bulletin of the American Meteorological Society. 90:1337-1350.   10.1175/2009bams2706.1   AbstractWebsite
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Andersson, AJ, Mackenzie FT, Lerman A.  2005.  Coastal ocean and carbonate systems in the high CO(2) world of the anthropocene. American Journal of Science. 305:875-918.   10.2475/ajs.305.9.875   AbstractWebsite

The behavior of the ocean carbon cycle has been, and will continue to be, modified by the increase in atmospheric CO(2) due to fossil fuel combustion and land-use emissions of this gas. The consequences of a high-CO(2) world and increasing riverine transport of organic matter and nutrients arising from human activities were investigated by means of two biogeochemical box models. Model numerical simulations ranging from the year 1700 to 2300 show that the global coastal ocean changes from a net source to a net sink of atmospheric CO(2) over time; in the 18th and 19th centuries, the direction of the CO(2) flux was from coastal surface waters to the atmosphere, whereas at present or in the near future the net CO(2) flux is into coastal surface waters. These results agree well with recent syntheses of measurements of air-sea CO(2) exchange fluxes from various coastal ocean environments. The model calculations also show that coastal ocean surface water carbonate saturation state would decrease 46 percent by the year 2100 and 73 percent by 2300. Observational evidence from the Pacific and Atlantic Oceans shows that die carbonate saturation state of surface ocean waters has already declined during recent decades. For atolls and other semi-enclosed carbonate systems, the rate of decline depends strongly on the residence time of the water in the system. Based on the experimentally observed positive relationship between saturation state and calcification rate for many calcifying organisms, biogenic production of CaCO(3) may decrease by 42 percent by the year 2100 and by 85 to 90 percent by 2300 relative to its value of about 24 x 10(12) moles C/yr in the year 2000. If the predicted change in carbonate production were to occur along with rising temperatures, it would make it difficult for coral reef and other carbonate systems, to exist as we know them now into future centuries. Because high-latitude, cold-water carbonates presently occur in waters closer to saturation with respect to carbonate minerals than the more strongly supersaturated waters of the lower latitudes, it might be anticipated that the cool-water carbonate systems might feel the effects of rising atmospheric CO(2) (and temperature) before those at lower latitudes. In addition, modeling results show that the carbonate saturation state of coastal sediment pore water will decrease in the future owing to a decreasing pore water pH and increasing CO(2) concentrations attributable to greater deposition and remineralization of land-derived and in situ produced organic matter in sediments. The lowered carbonate saturation state drives selective dissolution of metastable carbonate minerals while a metastable equilibrium is maintained between the pore water and the most soluble carbonate phase present in the sediments. In the future, the average composition of carbonate sediments and cements may change as the more soluble Mg-calcites and aragonite are preferentially dissolved and phases of lower solubility, such as calcites with lower magnesium content, increase in percentage abundance in the sediments.

Andersson, AJ, Mackenzie FT, Lerman A.  2006.  Coastal ocean CO(2)-carbonic acid-carbonate sediment system of the Anthropocene. Global Biogeochemical Cycles. 20   10.1029/2005gb002506   AbstractWebsite

[1] There is little doubt that human activities such as burning of fossil fuels and land use practices have changed and will continue to change the cycling of carbon in the global coastal ocean. In the present study, two biogeochemical box models were used to investigate the consequences of increasing atmospheric CO(2) and subsequent ocean acidification and increasing riverine transport of organic matter and nutrients arising from human activities on land on the global coastal ocean between the years 1700 and 2300. Numerical simulations show that the net flux of CO(2) between coastal ocean surface water and the atmosphere is likely to change during this time from net evasion to net invasion owing to increasing atmospheric CO(2), increasing net ecosystem production arising from increasing nutrient loading to this region, and decreasing net ecosystem calcification due to lower carbonate ion concentration and subsequent lower surface water saturation state with respect to carbonate minerals. Model calculations show that surface water saturation state with respect to calcite will decrease 73% by the year 2300 under a business-as-usual scenario, which in concert with increasing temperature will cause overall biogenic calcification rate to decrease by 90%. Dissolution of carbonate minerals increased by 267% throughout the model simulation. This increase was in part due to increased invasion of atmospheric CO(2), but mainly due to greater deposition and remineralization of land-derived and in situ produced organic matter in the sediments, producing CO(2) that caused pore water pH and carbonate saturation state to decrease. This decrease, in turn, drove selective dissolution of metastable carbonate minerals. As a consequence, the relative carbonate composition of the sediments changed in favor of carbonate phases with lower solubility than that of an average 15 mol% magnesian calcite phase. Model projected changes in surface water carbonate saturation state agree well with observations from the Hawaiian Ocean Time series and the calculated air-sea CO(2) exchanged agrees well with a recent independent estimate of this flux derived from measurements from diverse coastal ecosystems scaled up to the global coastal ocean area.

Lerman, A, Guidry M, Andersson AJ, Mackenzie FT.  2011.  Coastal Ocean Last Glacial Maximum to 2100 CO(2)-Carbonic Acid-Carbonate System: A Modeling Approach. Aquatic Geochemistry. 17:749-773.   10.1007/s10498-011-9146-z   AbstractWebsite

Using coupled terrestrial and coastal zone models, we investigated the impacts of deglaciation and anthropogenic inputs on the CO(2)-H(2)O-CaCO(3) system in global coastal ocean waters from the Last Glacial Maximum (LGM: 18,000 year BP) to the year 2100. With rising sea level and atmospheric CO(2), the carbonate system of coastal ocean water changed significantly. We find that 6 x 10(12) metric tons of carbon were emitted from the coastal ocean, growing due to the sea level rise, from the LGM to late preindustrial time (1700 AD) because of net heterotrophy and calcification processes. This carbon came to reside in the atmosphere and in the growing vegetation on land and in uptake of atmospheric CO(2) through the weathering of rocks on land. It appears that carbonate accumulation, mainly, but not exclusively, in coral reefs from the LGM to late preindustrial time could account for about 24 ppmv of the 100 ppmv rise in atmospheric CO(2), lending some support to the "coral reef hypothesis". In addition, the global coastal ocean is now, or soon will be, a sink of atmospheric CO(2). The temperature rise of 4-5A degrees C since the LGM led to increased weathering rates of inorganic and organic materials on land and enhanced riverine fluxes of total C, N, and P to the coastal ocean of 68%, 108%, and 97%, respectively, from the LGM to late preindustrial time. During the Anthropocene, these trends have been exacerbated owing to rising atmospheric CO(2), due to fossil fuel combustion and land-use practices, other human activities, and rising global temperatures. River fluxes of total reactive C, N, and P are projected to increase from late preindustrial time to the year 2100 by 150%, 380%, and 257%, respectively, modifying significantly the behavior of these element cycles in the coastal ocean, particularly in proximal environments. Despite the fact that the global shoal water carbonate mass has grown extensively since the LGM, the pH(T) (pH values on the total proton scale) of global coastal waters has decreased from similar to 8.35 to similar to 8.18 and the carbonate ion concentration declined by similar to 19% from the LGM to late preindustrial time. The latter represents a rate of decline of about 0.028 mu mol CO(3) (2-) per decade. In comparison, the decrease in coastal water pH(T) from the year 1900 to 2000 was about 8.18-8.08 and is projected to decrease further from about 8.08 to 7.85 between 2000 and 2100, according to the IS92a business-as-usual scenario of CO(2) emissions. Over these 200 years, the carbonate ion concentration will fall by similar to 120 mu mol kg(-1) or 6 mu mol kg(-1) per decade. This decadal rate of decline of the carbonate ion concentration in the Anthropocene is 214 times the average rate of decline for the entire Holocene. Hence, when viewed against the millennial to several millennial timescale of geologic change in the coastal ocean marine carbon system, one can easily appreciate why ocean acidification is the "other CO(2) problem".

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Page, HN, Andersson AJ, Jokiel PL, Rodgers K’uleiS, Lebrato M, Yeakel K, Davidson C, D’Angelo S, Bahr KD.  2016.  Differential modification of seawater carbonate chemistry by major coral reef benthic communities. Coral Reefs. :1-15.   10.1007/s00338-016-1490-4   AbstractWebsite

Ocean acidification (OA) resulting from uptake of anthropogenic CO2 may negatively affect coral reefs by causing decreased rates of biogenic calcification and increased rates of CaCO3 dissolution and bioerosion. However, in addition to the gradual decrease in seawater pH and Ω a resulting from anthropogenic activities, seawater carbonate chemistry in these coastal ecosystems is also strongly influenced by the benthic metabolism which can either exacerbate or alleviate OA through net community calcification (NCC = calcification – CaCO3 dissolution) and net community organic carbon production (NCP = primary production − respiration). Therefore, to project OA on coral reefs, it is necessary to understand how different benthic communities modify the reef seawater carbonate chemistry. In this study, we used flow-through mesocosms to investigate the modification of seawater carbonate chemistry by benthic metabolism of five distinct reef communities [carbonate sand, crustose coralline algae (CCA), corals, fleshy algae, and a mixed community] under ambient and acidified conditions during summer and winter. The results showed that different communities had distinct influences on carbonate chemistry related to the relative importance of NCC and NCP. Sand, CCA, and corals exerted relatively small influences on seawater pH and Ω a over diel cycles due to closely balanced NCC and NCP rates, whereas fleshy algae and mixed communities strongly elevated daytime pH and Ω a due to high NCP rates. Interestingly, the influence on seawater pH at night was relatively small and quite similar across communities. NCC and NCP rates were not significantly affected by short-term acidification, but larger diel variability in pH was observed due to decreased seawater buffering capacity. Except for corals, increased net dissolution was observed at night for all communities under OA, partially buffering against nighttime acidification. Thus, algal-dominated areas of coral reefs and increased net CaCO3 dissolution may partially counteract reductions in seawater pH associated with anthropogenic OA at the local scale.

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Courtney, TA, Lebrato M, Bates NR, Collins A, de Putron SJ, Garley R, Johnson R, Molinero JC, Noyes TJ, Sabine CL, Andersson AJ.  2017.  Environmental controls on modern scleractinian coral and reef-scale calcification. Science Advances. 3   10.1126/sciadv.1701356   AbstractWebsite

Modern reef-building corals sustain a wide range of ecosystem services because of their ability to build calcium carbonate reef systems. The influence of environmental variables on coral calcification rates has been extensively studied, but our understanding of their relative importance is limited by the absence of in situ observations and the ability to decouple the interactions between different properties. We show that temperature is the primary driver of coral colony (Porites astreoides and Diploria labyrinthiformis) and reef-scale calcification rates over a 2-year monitoring period from the Bermuda coral reef. On the basis of multimodel climate simulations (Coupled Model Intercomparison Project Phase 5) and assuming sufficient coral nutrition, our results suggest that P. astreoides and D. labyrinthiformis coral calcification rates in Bermuda could increase throughout the 21st century as a result of gradual warming predicted under a minimum CO2 emissions pathway [ representative concentration pathway (RCP) 2.6] with positive 21st-century calcification rates potentially maintained under a reduced CO2 emissions pathway (RCP 4.5). These results highlight the potential benefits of rapid reductions in global anthropogenic CO2 emissions for 21st-century Bermuda coral reefs and the ecosystem services they provide.

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Guest, JR, Edmunds PJ, Gates RD, Kuffner IB, Andersson AJ, Barnes BB, Chollett I, Courtney TA, Elahi R, Gross K, Lenz EA, Mitarai S, Mumby PJ, Nelson HR, Parker BA, Putnam HM, Rogers CS, Toth LT.  2018.  A framework for identifying and characterising coral reef "oases" against a backdrop of degradation. Journal of Applied Ecology. 55:2865-2875.   10.1111/1365-2664.13179   AbstractWebsite

1. Human activities have led to widespread ecological decline; however, the severity of degradation is spatially heterogeneous due to some locations resisting, escaping, or rebounding from disturbances. 2. We developed a framework for identifying oases within coral reef regions using long-term monitoring data. We calculated standardised estimates of coral cover (z-scores) to distinguish sites that deviated positively from regional means. We also used the coefficient of variation (CV) of coral cover to quantify how oases varied temporally, and to distinguish among types of oases. We estimated "coral calcification capacity" (CCC), a measure of the coral community's ability to produce calcium carbonate structures and tested for an association between this metric and z-scores of coral cover. 3. We illustrated our z-score approach within a modelling framework by extracting z-scores and CVs from simulated data based on four generalized trajectories of coral cover. We then applied the approach to time-series data from long-term reef monitoring programmes in four focal regions in the Pacific (the main Hawaiian Islands and Mo'orea, French Polynesia) and western Atlantic (the Florida Keys and St. John, US Virgin Islands). Among the 123 sites analysed, 38 had positive z-scores for median coral cover and were categorised as oases. 4. Synthesis and applications. Our framework provides ecosystem managers with a valuable tool for conservation by identifying "oases" within degraded areas. By evaluating trajectories of change in state (e.g., coral cover) among oases, our approach may help in identifying the mechanisms responsible for spatial variability in ecosystem condition. Increased mechanistic understanding can guide whether management of a particular location should emphasise protection, mitigation or restoration. Analysis of the empirical data suggest that the majority of our coral reef oases originated by either escaping or resisting disturbances, although some sites showed a high capacity for recovery, while others were candidates for restoration. Finally, our measure of reef condition (i.e., median z-scores of coral cover) correlated positively with coral calcification capacity suggesting that our approach identified oases that are also exceptional for one critical component of ecological function.

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Reid, PC, Fischer AC, Lewis-Brown E, Meredith MP, Sparrow M, Andersson AJ, Antia A, Bates NR, Bathmann U, Beaugrand G, Brix H, Dye S, Edwards M, Furevik T, Gangsto R, Hatun H, Hopcroft RR, Kendall M, Kasten S, Keeling R, Le Quere C, Mackenzie FT, Malin G, Mauritzen C, Olafsson J, Paull C, Rignot E, Shimada K, Vogt M, Wallace C, Wang ZM, Washington R.  2009.  Impacts of the Oceans on Climate Change. Advances in Marine Biology, Vol 56. 56( Sims DW, Ed.).:1-150., San Diego: Elsevier Academic Press Inc   10.1016/s0065-2881(09)56001-4   Abstract

The oceans play a key role in climate regulation especially in part buffering (neutralising) the effects of increasing levels of greenhouse gases in the atmosphere and rising global temperatures. This chapter examines how the regulatory processes performed by the oceans alter as a response to climate change and assesses the extent to which positive feedbacks from the ocean may exacerbate climate change. There is clear evidence for rapid change in the oceans. As the main heat store for the world there has been an accelerating change in sea temperatures over the last few decades, which has contributed to rising sea-level. The oceans are also the main store of carbon dioxide (CO(2)), and are estimated to have taken up similar to 40% of anthropogenic-sourced CO(2) from the atmosphere since the beginning of the industrial revolution. A proportion of the carbon uptake is exported via the four ocean 'carbon pumps' (Solubility, Biological, Continental Shelf and Carbonate Counter) to the deep ocean reservoir. Increases in sea temperature and changing planktonic systems and ocean currents may lead to a reduction in the uptake of CO(2) by the ocean; some evidence suggests a suppression of parts of the marine carbon sink is already underway. While the oceans have buffered climate change through the uptake of CO(2) produced by fossil fuel burning this has already had an impact on ocean chemistry through ocean acidification and will continue to do so. Feedbacks to climate change from acidification may result from expected impacts on marine organisms (especially corals and calcareous plankton), ecosystems and biogeochemical cycles. The polar regions of the world are showing the most rapid responses to climate change. As a result of a strong ice-ocean influence, small changes in temperature, salinity and ice cover may trigger large and sudden changes in regional climate with potential downstream feedbacks to the climate of the rest of the world. A warming Arctic Ocean may lead to further releases of the potent greenhouse gas methane from hydrates and permafrost. The Southern Ocean plays a critical role in driving, modifying and regulating global climate change via the carbon cycle and through its impact on adjacent Antarctica. The Antarctic Peninsula has shown some of the most rapid rises in atmospheric and oceanic temperature in the world, with an associated retreat of the majority of glaciers. Parts of the West Antarctic ice sheet are deflating rapidly, very likely due to a change in the flux of oceanic heat to the undersides of the floating ice shelves. The final section on modelling feedbacks from the ocean to climate change identifies limitations and priorities for model development and associated observations. Considering the importance of the oceans to climate change and our limited understanding of climate-related ocean processes, our ability to measure the changes that are taking place are conspicuously inadequate. The chapter highlights the need for a comprehensive, adequately funded and globally extensive ocean observing system to be implemented and sustained as a high priority. Unless feedbacks from the oceans to climate change are adequately included in climate change models, it is possible that the mitigation actions needed to stabilise CO(2) and limit temperature rise over the next century will be underestimated.

Edmunds, PJ, Comeau S, Lantz C, Andersson A, Briggs C, Cohen A, Gattuso JP, Grady JM, Gross K, Johnson M, Muller EB, Ries JB, Tambutte S, Tambutte E, Venn A, Carpenter RC.  2016.  Integrating the effects of ocean acidification across functional scales on tropical coral reefs. Bioscience. 66:350-362.   10.1093/biosci/biw023   AbstractWebsite

There are concerns about the future of coral reefs in the face of ocean acidification and warming, and although studies of these phenomena have advanced quickly, efforts have focused on pieces of the puzzle rather than integrating them to evaluate ecosystem-level effects. The field is now poised to begin this task, but there are information gaps that first must be overcome before progress can be made. Many of these gaps focus on calcification at the levels of cells, organisms, populations, communities, and ecosystem, and their closure will be made difficult by the complexity of the interdependent processes by which coral reefs respond to ocean acidification, with effects scaling from cells to ecosystems and from microns to kilometers. Existing ecological theories provide an important and largely untapped resource for overcoming these difficulties, and they offer great potential for integrating the effects of ocean acidification across scales on coral reefs.

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Mackenzie, FT, Andersson AJ, Arvidson RS, Guidry MW, Lerman A.  2011.  Land-sea carbon and nutrient fluxes and coastal ocean CO(2) exchange and acidification: Past, present, and future. Applied Geochemistry. 26:S298-S302.   10.1016/j.apgeochem.2011.03.087   AbstractWebsite

Epochs of changing atmospheric CO(2) and seawater CO(2)-carbonic acid system chemistry and acidification have occurred during the Phanerozoic at various time scales. On the longer geologic time scale, as sea level rose and fell and continental free board decreased and increased, respectively, the riverine fluxes of Ca, Mg, DIC, and total alkalinity to the coastal ocean varied and helped regulate the C chemistry of seawater, but nevertheless there were major epochs of ocean acidification (OA). On the shorter glacial-interglacial time scale from the Last Glacial Maximum (LGM) to late preindustrial time, riverine fluxes of DIC, total alkalinity, and N and P nutrients increased and along with rising sea level, atmospheric PCO(2) and temperature led, among other changes, to a slightly deceasing pH of coastal and open ocean waters, and to increasing net ecosystem calcification and decreasing net heterotrophy in coastal ocean waters. From late preindustrial time to the present and projected into the 21st century, human activities, such as fossil fuel and land-use emissions of CO(2) to the atmosphere, increasing application of N and P nutrient subsidies and combustion N to the landscape, and sewage discharges of C, N, P have led, and will continue to lead, to significant modifications of coastal ocean waters. The changes include a rapid decline in pH and carbonate saturation state (modern problem of ocean acidification), a shift toward dissolution of carbonate substrates exceeding production, potentially leading to the "demise" of the coral reefs, reversal of the direction of the sea-to-air flux of CO(2) and enhanced biological production and burial of organic C, a small sink of anthropogenic CO(2), accompanied by a continuous trend toward increasing autotrophy in coastal waters. (C) 2011 Elsevier Ltd. All rights reserved.

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Langdon, CR, Gatusso JP, Andersson AJ.  2010.  Measurements of calcification abd dissolution of benthic organisms and communities. Guidebest practices in ocean acidification Reserach and data reporting . Abstract
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Venti, A, Kadko D, Andersson AJ, Langdon C, Bates NR.  2012.  A multi-tracer model approach to estimate reef water residence times. Limnology and Oceanography-Methods. 10:1078-1095.   10.4319/lom.2012.10.1078   AbstractWebsite

We present a new method for obtaining the residence time of coral reef waters and demonstrate the successful application of this method by estimating rates of net ecosystem calcification (NEC) at four locations across the Bermuda platform and showing that the rates thus obtained are in reasonable agreement with independent estimates based on different methodologies. The contrast in Be-7 activity between reef and offshore waters can be related to the residence time of the waters over the reef through a time-dependent model that takes into account the rainwater flux of Be-7, the radioactive half-life of Be-7, and the rate of removal of Be-7 on particles estimated from Th-234. Sampling for Be-7 and Th-234 was conducted during the late fall and winter between 2008 and 2010. Model results yielded residence times ranging from 1.4 (+/- 0.7) days at the rim reef to 12 (+/- 4.0) days closer to shore. When combined with measurements of salinity-normalized total alkalinity anomalies, these residence times yielded platform-average NEC rates ranging from a maximum of 20.3 (+/- 7.0) mmolCaCO(3) m(-2) d(-1) in Nov 2008 to a minimum of 2.5 (+/- 0.8) mmolCaCO(3) m(-2) d(-1) in Feb 2009. The advantage of this new approach is that the rates of NEC obtained are temporally and spatially averaged. This novel approach for estimating NEC rates may be applicable to other coral reef ecosystems, providing an opportunity to assess how these rates may change in the context of ocean acidification.

Venti, A, Andersson A, Langdon C.  2014.  Multiple driving factors explain spatial and temporal variability in coral calcification rates on the Bermuda platform. Coral Reefs. 33:979-997.   10.1007/s00338-014-1191-9   AbstractWebsite

Experimental studies have shown that coral calcification rates are dependent on light, nutrients, food availability, temperature, and seawater aragonite saturation (Omega (arag)), but the relative importance of each parameter in natural settings remains uncertain. In this study, we applied Calcein fluorescent dyes as time indicators within the skeleton of coral colonies (n = 3) of Porites astreoides and Diploria strigosa at three study sites distributed across the northern Bermuda coral reef platform. We evaluated the correlation between seasonal average growth rates based on coral density and extension rates with average temperature, light, and seawater Omega (arag) in an effort to decipher the relative importance of each parameter. The results show significant seasonal differences among coral calcification rates ranging from summer maximums of 243 +/- A 58 and 274 +/- A 57 mmol CaCO3 m(-2) d(-1) to winter minimums of 135 +/- A 39 and 101 +/- A 34 mmol CaCO3 m(-2) d(-1) for P. astreoides and D. strigosa, respectively. We also placed small coral colonies (n = 10) in transparent chambers and measured the instantaneous rate of calcification under light and dark treatments at the same study sites. The results showed that the skeletal growth of D. strigosa and P. astreoides, whether hourly or seasonal, was highly sensitive to Omega (arag). We believe this high sensitivity, however, is misleading, due to covariance between light and Omega (arag), with the former being the strongest driver of calcification variability. For the seasonal data, we assessed the impact that the observed seasonal differences in temperature (4.0 A degrees C), light (5.1 mol photons m(-2) d(-1)), and Omega (arag) (0.16 units) would have on coral growth rates based on established relationships derived from laboratory studies and found that they could account for approximately 44, 52, and 5 %, respectively, of the observed seasonal change of 81 +/- A 14 mmol CaCO3 m(-2) d(-1). Using short-term light and dark incubations, we show how the covariance of light and Omega (arag) can lead to the false conclusion that calcification is more sensitive to Omega (arag) than it really is.

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Mackenzie, FT, Lerman A, Andersson AJ.  2004.  Past and present of sediment and carbon biogeochemical cycling models. Biogeosciences. 1:11-32. AbstractWebsite

The global carbon cycle is part of the much more extensive sedimentary cycle that involves large masses of carbon in the Earth's inner and outer spheres. Studies of the carbon cycle generally followed a progression in knowledge of the natural biological, then chemical, and finally geological processes involved, culminating in a more or less integrated picture of the biogeochemical carbon cycle by the 1920s. However, knowledge of the ocean's carbon cycle behavior has only within the last few decades progressed to a stage where meaningful discussion of carbon processes on an annual to millennial time scale can take place. In geologically older and pre-industrial time, the ocean was generally a net source of CO2 emissions to the atmosphere owing to the mineralization of land-derived organic matter in addition to that produced in situ and to the process of CaCO3 precipitation. Due to rising atmospheric CO2 concentrations because of fossil fuel combustion and land use changes, the direction of the air-sea CO2 flux has reversed, leading to the ocean as a whole being a net sink of anthropogenic CO2. The present thickness of the surface ocean layer, where part of the anthropogenic CO2 emissions are stored, is estimated as of the order of a few hundred meters. The oceanic coastal zone net air-sea CO2 exchange flux has also probably changed during industrial time. Model projections indicate that in preindustrial times, the coastal zone may have been net heterotrophic, releasing CO2 to the atmosphere from the imbalance between gross photosynthesis and total respiration. This, coupled with extensive CaCO3 precipitation in coastal zone environments, led to a net flux of CO2 out of the system. During industrial time the coastal zone ocean has tended to reverse its trophic status toward a non-steady state situation of net autotrophy, resulting in net uptake of anthropogenic CO2 and storage of carbon in the coastal ocean, despite the significant calcification that still occurs in this region. Furthermore, evidence from the inorganic carbon cycle indicates that deposition and net storage of CaCO3 in sediments exceed inflow of inorganic carbon from land and produce CO2 emissions to the atmosphere. In the shallow-water coastal zone, increase in atmospheric CO2 during the last 300 years of industrial time may have reduced the rate of calcification, and continuation of this trend is an issue of serious environmental concern in the global carbon balance.

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Sato, KN, Andersson AJ, Day JMD, Taylor JRA, Frank MB, Jung JY, McKittrick J, Levin LA.  2018.  Response of sea urchin fitness traits to environmental gradients across the Southern California oxygen minimum zone. Frontiers in Marine Science. 5   10.3389/fmars.2018.00258   AbstractWebsite

Marine calcifiers are considered to be among the most vulnerable taxa to climate-forced environmental changes occurring on continental margins with effects hypothesized to occur on microstructural, biomechanical, and geochemical properties of carbonate structures. Natural gradients in temperature, salinity, oxygen, and pH on an upwelling margin combined with the broad depth distribution (100-1,100 m) of the pink fragile sea urchin, Strongylocentrotus (formerly Allocentrotus) fragilis, along the southern California shelf and slope provide an ideal system to evaluate potential effects of multiple climate variables on carbonate structures in situ. We measured, for the first time, trait variability across four distinct depth zones using natural gradients as analogues for species-specific implications of oxygen minimum zone (OMZ) expansion, deoxygenation and ocean acidification. Although S. fragilis may likely be tolerant of future oxygen and pH decreases predicted during the twenty-first century, we determine from adults collected across multiple depth zones that urchin size and potential reproductive fitness (gonad index) are drastically reduced in the OMZ core (450-900 m) compared to adjacent zones. Increases in porosity and mean pore size coupled with decreases in mechanical nanohardness and stiffness of the calcitic endoskeleton in individuals collected from lower pH(Total) (7.57-7.59) and lower dissolved oxygen (13-42 mu mol kg(-1)) environments suggest that S. fragilis may be potentially vulnerable to crushing predators if these conditions become more widespread in the future. In addition, elemental composition indicates that S. fragilis has a skeleton composed of the low Mg-calcite mineral phase of calcium carbonate (mean Mg/Ca = 0.02 mol mol(-1)), with Mg/Ca values measured in the lower end of values reported for sea urchins known to date. Together these findings suggest that ongoing declines in oxygen and pH will likely affect the ecology and fitness of a dominant echinoid on the California margin.

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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.

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Cyronak, T, Andersson AJ, Langdon C, Albright R, Bates NR, Caldeira K, Carlton R, Corredor JE, Dunbar RB, Enochs I, Erez J, Eyre BD, Gattuso JP, Gledhill D, Kayanne H, Kline DI, Koweek DA, Lantz C, Lazar B, Manzello D, McMahon A, Melendez M, Page HN, Santos IR, Schulz KG, Shaw E, Silverman J, Suzuki A, Teneva L, Watanabe A, Yamamoto S.  2018.  Taking the metabolic pulse of the world's coral reefs. Plos One. 13   10.1371/journal.pone.0190872   AbstractWebsite

Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of anthropogenic perturbations including ocean warming and acidification, increased sedimentation, eutrophication, and overfishing, which could shift reefs to a condition of net calcium carbonate (CaCO3) dissolution and erosion. Herein, we determine the net calcification potential and the relative balance of net organic carbon metabolism (net community production; NCP) and net inorganic carbon metabolism (net community calcification; NCC) within 23 coral reef locations across the globe. In light of these results, we consider the suitability of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected on different spatiotemporal scales to monitor coral reef biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However, reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net dissolution sooner than reefs with a higher potential. The percent influence of organic carbon fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences between reefs. Reefs with the largest relative percentage of NCP experienced the largest variability in seawater pH for a given change in DIC, which is directly related to the reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to ongoing global environmental change and offers a baseline from which to guide future conservation efforts aimed at preserving these valuable ecosystems.