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Andersson, AJ, Bates NR, Mackenzie FT.  2007.  Dissolution of carbonate sediments under rising pCO(2) and ocean acidification: Observations from Devil's Hole, Bermuda. Aquatic Geochemistry. 13:237-264.   10.1007/s10498-007-9018-8   AbstractWebsite

Rising atmospheric pCO(2) and ocean acidification originating from human activities could result in increased dissolution of metastable carbonate minerals in shallow-water marine sediments. In the present study, in situ dissolution of carbonate sedimentary particles in Devil's Hole, Bermuda, was observed during summer when thermally driven density stratification restricted mixing between the bottom water and the surface mixed layer and microbial decomposition of organic matter in the subthermocline layer produced pCO(2) levels similar to or higher than those levels anticipated by the end of the 21st century. Trends in both seawater chemistry and the composition of sediments in Devil's Hole indicate that Mg-calcite minerals are subject to selective dissolution under conditions of elevated pCO(2). The derived rates of dissolution based on observed changes in excess alkalinity and estimates of vertical eddy diffusion ranged from 0.2 mmol to 0.8 mmol CaCO3 m(-2) h(-1). On a yearly basis, this range corresponds to 175-701 g CaCO3 m(-2) year(-1); the latter rate is close to 50% of the estimate of the current average global coral reef calcification rate of about 1,500 g CaCO3 m(-2) year(-1). Considering a reduction in marine calcification of 40% by the year 2100, or 90% by 2300, as a result of surface ocean acidification, the combination of high rates of carbonate dissolution and reduced rates of calcification implies that coral reefs and other carbonate sediment environments within the 21st and following centuries could be subject to a net loss in carbonate material as a result of increasing pCO(2) arising from burning of fossil fuels.

Jokiel, PL, Rodgers KS, Kuffner IB, Andersson AJ, Cox EF, Mackenzie FT.  2008.  Ocean acidification and calcifying reef organisms: a mesocosm investigation. Coral Reefs. 27:473-483.   10.1007/s00338-008-0380-9   AbstractWebsite

A long-term (10 months) controlled experiment was conducted to test the impact of increased partial pressure of carbon dioxide (pCO(2)) on common calcifying coral reef organisms. The experiment was conducted in replicate continuous flow coral reef mesocosms flushed with unfiltered sea water from Kaneohe Bay, Oahu, Hawaii. Mesocosms were located in full sunlight and experienced diurnal and seasonal fluctuations in temperature and sea water chemistry characteristic of the adjacent reef flat. Treatment mesocosms were manipulated to simulate an increase in pCO(2) to levels expected in this century [midday pCO(2) levels exceeding control mesocosms by 365 +/- 130 mu atm (mean +/- sd)]. Acidification had a profound impact on the development and growth of crustose coralline algae (CCA) populations. During the experiment, CCA developed 25% cover in the control mesocosms and only 4% in the acidified mesocosms, representing an 86% relative reduction. Free-living associations of CCA known as rhodoliths living in the control mesocosms grew at a rate of 0.6 g buoyant weight year(-1) while those in the acidified experimental treatment decreased in weight at a rate of 0.9 g buoyant weight year(-1), representing a 250% difference. CCA play an important role in the growth and stabilization of carbonate reefs, so future changes of this magnitude could greatly impact coral reefs throughout the world. Coral calcification decreased between 15% and 20% under acidified conditions. Linear extension decreased by 14% under acidified conditions in one experiment. Larvae of the coral Pocillopora damicornis were able to recruit under the acidified conditions. In addition, there was no significant difference in production of gametes by the coral Montipora capitata after 6 months of exposure to the treatments.

Andersson, AJ, Kuffner IB, Mackenzie FT, Jokiel PL, Rodgers KS, Tan A.  2009.  Net Loss of CaCO(3) from a subtropical calcifying community due to seawater acidification: mesocosm-scale experimental evidence. Biogeosciences. 6:1811-1823. AbstractWebsite

Acidification of seawater owing to oceanic uptake of atmospheric CO(2) originating from human activities such as burning of fossil fuels and land-use changes has raised serious concerns regarding its adverse effects on corals and calcifying communities. Here we demonstrate a net loss of calcium carbonate (CaCO(3)) material as a result of decreased calcification and increased carbonate dissolution from replicated subtropical coral reef communities (n=3) incubated in continuous-flow mesocosms subject to future seawater conditions. The calcifying community was dominated by the coral Montipora capitata. Daily average community calcification or Net Ecosystem Calcification (NEC=CaCO(3) production - dissolution) was positive at 3.3 mmol CaCO(3) m(-2) h(-1) under ambient seawater pCO(2) conditions as opposed to negative at -0.04 mmol CaCO(3) m(-2) h(-1) under seawater conditions of double the ambient pCO(2). These experimental results provide support for the conclusion that some net calcifying communities could become subject to net dissolution in response to anthropogenic ocean acidification within this century. Nevertheless, individual corals remained healthy, actively calcified (albeit slower than at present rates), and deposited significant amounts of CaCO(3) under the prevailing experimental seawater conditions of elevated pCO(2).

Andersson, AJ, Mackenzie FT.  2011.  Technical comment on Kroeker et al. (2010) Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology Letters, 13, 1419–1434. Ecology Letters. 14:E1-E2.: Blackwell Publishing Ltd   10.1111/j.1461-0248.2011.01646.x   AbstractWebsite

Meta-analysis of experimental results has been interpreted to imply that the calcification response of organisms depositing high Mg-calcite is more resilient to ocean acidification than organisms depositing aragonite/calcite. This conclusion might be biased by inadequate recognition and categorisation of high Mg-calcite according to mineral solubility.

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".

Kuffner, IB, Jokiel PL, Rodgers KS, Andersson AJ, Mackenzie FT.  2012.  An apparent "vital effect" of calcification rate on the Sr/Ca temperature proxy in the reef coral Montipora capitata. Geochemistry Geophysics Geosystems. 13   10.1029/2012gc004128   AbstractWebsite

Measuring the strontium to calcium ratio in coral skeletons reveals information on seawater temperatures during skeletal deposition, but studies have shown additional variables may affect the ratio. Here we measured Sr/Ca in the reef coral Montipora capitata grown in six mesocosms continuously supplied with seawater from the adjacent reef flat. Three mesocosms were ambient controls, and three had seawater chemistry simulating "ocean acidification" (OA). We found that Sr/Ca was not affected by the OA treatment and neither was coral calcification for these small colonies (larger colonies did show an OA effect). The lack of OA effects allowed us to test the hypothesis that coral growth rate can affect Sr/Ca using the natural range in calcification rates of the corals grown at the same temperature. We found that Sr/Ca was inversely related to calcification rate (Sr/Ca = 9.385 - 0.0040 (calcification rate)). Using a previously published calibration curve for this species, a 22 mg d(-1) colony(-1) increase in calcification rate introduced a 1 degrees C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9 degrees C, with mean 26.6 +/- 0.9 degrees C standard deviation. Our results lend support to hypotheses invoking kinetic processes and growth rate to explain vital effects on Sr/Ca. However, uncertainty in the slope of the regression of Sr/Ca on calcification and a low R-squared value lead us to conclude that Sr/Ca could still be a useful proxy in this species given sufficient replication or by including growth rate in the calibration.

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.

Yeakel, KL, Andersson AJ, Bates NR, Noyes TJ, Collins A, Garley R.  2015.  Shifts in coral reef biogeochemistry and resulting acidification linked to offshore productivity. Proceedings of the National Academy of Sciences of the United States of America. 112:14512-14517.   10.1073/pnas.1507021112   AbstractWebsite

Oceanic uptake of anthropogenic carbon dioxide (CO2) has acidified open-ocean surface waters by 0.1 pH units since preindustrial times. Despite unequivocal evidence of ocean acidification (OA) via open-ocean measurements for the past several decades, it has yet to be documented in near-shore and coral reef environments. A lack of long-term measurements from these environments restricts our understanding of the natural variability and controls of seawater CO2-carbonate chemistry and biogeochemistry, which is essential to make accurate predictions on the effects of future OA on coral reefs. Here, in a 5-y study of the Bermuda coral reef, we show evidence that variations in reef biogeochemical processes drive interannual changes in seawater pH and Omega(aragonite) that are partly controlled by offshore processes. Rapid acidification events driven by shifts toward increasing net calcification and net heterotrophy were observed during the summers of 2010 and 2011, with the frequency and extent of such events corresponding to increased offshore productivity. These events also coincided with a negative winter North Atlantic Oscillation (NAO) index, which historically has been associated with extensive offshore mixing and greater primary productivity at the Bermuda Atlantic Time-series Study (BATS) site. Our results reveal that coral reefs undergo natural interannual events of rapid acidification due to shifts in reef biogeochemical processes that may be linked to offshore productivity and ultimately controlled by larger-scale climatic and oceanographic processes.

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.

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.

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.

Eyre, BD, Cyronak T, Drupp P, DeCarlo EH, Sachs JP, Andersson AJ.  2018.  Coral reefs will transition to net dissolving before end of century. Science. 359:908-911.   10.1126/science.aao1118   AbstractWebsite

Ocean acidification refers to the lowering of the ocean's pH due to the uptake of anthropogenic CO2 from the atmosphere. Coral reef calcification is expected to decrease as the oceans become more acidic. Dissolving calciumcarbonate (CaCO3) sands could greatly exacerbate reef loss associated with reduced calcification but is presently poorly constrained. Here we show that CaCO3 dissolution in reef sediments across five globally distributed sites is negatively correlated with the aragonite saturation state (War) of overlying seawater and that CaCO3 sediment dissolution is 10-fold more sensitive to ocean acidification than coral calcification. Consequently, reef sediments globally will transition from net precipitation to net dissolution when seawater War reaches 2.92 +/- 0.16 (expected circa 2050 CE). Notably, some reefs are already experiencing net sediment dissolution.

MeQuaid, JB, Kustka AB, Obornik M, Horak A, McCrow JR, Karas BJ, Zheng H, Kindeberg T, Andersson AJ, Barbeau KA, Allen AE.  2018.  Carbonate-sensitive phytotransferrin controls high-affinity iron uptake in diatoms. Nature. 555:534-+.   10.1038/nature25982   AbstractWebsite

In vast areas of the ocean, the scarcity of iron controls the growth and productivity of phytoplankton(1,2). Although most dissolved iron in the marine environment is complexed with organic molecules(3), picomolar amounts of labile inorganic iron species (labile iron) are maintained within the euphotic zone(4) and serve as an important source of iron for eukaryotic phytoplankton and particularly for diatoms(5). Genome-enabled studies of labile iron utilization by diatoms have previously revealed novel iron responsive transcripts(6,7), including the ferric iron-concentrating protein ISIP2A(8), but the mechanism behind the acquisition of picomolar labile iron remains unknown. Here we show that ISIP2A is a phytotransferrin that independently and convergently evolved carbonate ion-coordinated ferric iron binding. Deletion of ISIP2A disrupts high-affinity iron uptake in the diatom Phaeodactylum tricornutum, and uptake is restored by complementation with human transferrin. ISIP2A is internalized by endocytosis, and manipulation of the seawater carbonic acid system reveals a second order dependence on the concentrations of labile iron and carbonate ions. In P. tricornutum, the synergistic interaction of labile iron and carbonate ions occurs at environmentally relevant concentrations, revealing that carbonate availability co-limits iron uptake. Phytotransferrin sequences have a broad taxonomic distribution(8) and are abundant in marine environmental genomic datasets(9,10), suggesting that acidification-driven declines in the concentration of seawater carbonate ions will have a negative effect on this globally important eukaryotic iron acquisition mechanism.

Takeshita, Y, Cyronak T, Martz TR, Kindeberg T, Andersson AJ.  2018.  Coral reef carbonate chemistry variability at different functional scales. Frontiers in Marine Science. 5   10.3389/fmars.2018.00175   AbstractWebsite

There is a growing recognition for the need to understand how seawater carbonate chemistry over coral reef environments will change in a high-CO2 world to better assess the impacts of ocean acidification on these valuable ecosystems. Coral reefs modify overlying water column chemistry through biogeochemical processes such as net community organic carbon production (NCR) and calcification (NCC). However, the relative importance and influence of these processes on seawater carbonate chemistry vary across multiple functional scales (defined here as space, time, and benthic community composition), and have not been fully constrained. Here, we use Bermuda as a case study to assess (1) spatiotemporal variability in physical and chemical parameters along a depth gradient at a rim reef location, (2) the spatial variability of total alkalinity (TA) and dissolved inorganic carbon (DIC) over distinct benthic habitats to infer NCC:NCP ratios [< several km(2); rim reef vs. seagrass and calcium carbonate (CaCO3) sediments] on diel timescales, and (3) compare how TA-DIC relationships and NCC:NCP vary as we expand functional scales from local habitats to the entire reef platform (10's of km(2)) on seasonal to interannual timescales. Our results demonstrate that TA-DIC relationships were strongly driven by local benthic metabolism and community composition over diel cycles. However, as the spatial scale expanded to the reef platform, the TA-DIC relationship reflected processes that were integrated over larger spatiotemporal scales, with effects of NCC becoming increasingly more important over NCR. This study demonstrates the importance of considering drivers across multiple functional scales to constrain carbonate chemistry variability over coral reefs.

Cyronak, T, Andersson AJ, D'Angelo S, Bresnahan P, Davidson C, Griffin A, Kindeberg T, Pennise J, Takeshita Y, White M.  2018.  Short-term spatial and temporal carbonate chemistry variability in two contrasting seagrass meadows: Implications for pH buffering capacities. Estuaries and Coasts. 41:1282-1296.   10.1007/s12237-017-0356-5   AbstractWebsite

It has been hypothesized that highly productive coastal ecosystems, such as seagrass meadows, could lead to the establishment of ocean acidification (OA) refugia, or areas of elevated pH and aragonite saturation state (Omega(a)) compared to source seawater. However, seagrass ecosystems experience extreme variability in carbonate chemistry across short temporal and small spatial scales, which could impact the pH buffering capacity of these potential refugia. Herein, short-term (hourly to diel) and small-scale (across 0.01-0.14 km(2)) spatiotemporal carbonate chemistry variability was assessed within two seagrass meadows in order to determine their short-term potential to elevate seawater pH relative to source seawater. Two locations at similar latitudes were chosen in order to compare systems dominated by coarse calcium carbonate (Bailey's Bay, Bermuda) and muddy silicate (Mission Bay, CA, USA) sediments. In both systems, spatial variability of pH across the seagrass meadow at any given time was often greater than diel variability (e.g., the average range over 24 h) at any one site, with greater spatial variability occurring at low tide in Mission Bay. Mission Bay (spatial Delta pH = 0.08 +/- 0.08; diel Delta pH = 0.12 +/- 0.01; mean +/- SD) had a greater average range in both temporal and spatial seawater chemistry than Bailey's Bay (spatial Delta pH = 0.02 +/- 0.01; diel Delta pH = 0.03 +/- 0.00; mean +/- SD). These differences were most likely due to a combination of slower currents, a larger tidal range, and more favorable weather conditions for photosynthesis (e.g., sunny with no rain) in Mission Bay. In both systems, there was a substantial amount of time (usually at night) when seawater pH within the seagrass beds was lower relative to the source seawater. Future studies aimed at assessing the potential of seagrass ecosystems to act as OA refugia for marine organisms need to account for the small-scale, high-frequency carbonate chemistry variability in both space and time, as this variability will impact where and when OA will be buffered or intensified.

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.

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.// (Sutton et al., 2018).