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Andersson, AJ, Mackenzie FT.  2004.  Shallow-water oceans: a source or sink of atmospheric CO2? Frontiers in Ecology and the Environment. 2:348-353.   10.1890/1540-9295(2004)002[0348:soasos];2   AbstractWebsite

The shallow-water ocean environment is of great importance in the context of global change and is heavily impacted by human activity. This study evaluates the effects of human activity on the CO2 exchange between the atmosphere and the surface water of shallow-water oceans. The evaluation is based on changes in net ecosystem metabolism, net ecosystem calcification, and atmospheric CO2 concentrations, as seen in a process-driven biogeochemical box model. Numerical simulations show that this air-sea interface has probably served as a net source of CO2 to the atmosphere for much of the past 300 years, but has recently switched, or will switch soon, to a net sink of CO2, because of rising atmospheric CO2 and increasing inorganic nutrient load.

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.

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.

Andersson, AJ, Mackenzie FT, Ver LM.  2003.  Solution of shallow-water carbonates: An insignificant buffer against rising atmospheric CO2. Geology. 31:513-516.   10.1130/0091-7613(2003)031<0513:soscai>;2   AbstractWebsite

Model predictions suggest that the saturation state of surface ocean waters with respect to carbonate minerals will decline during the twenty-first century owing to increased invasion of atmospheric CO2. As a result, calcareous organisms may have difficulty calcifying, leading to production of weaker skeletons and greater vulnerability to erosion. Alternatively, it has been suggested that there will be no significant impact on coral reef ecosystems because any changes in saturation state and pH will be restored by dissolution of metastable carbonate minerals. To resolve this controversy, we employ a physical-biogeochemical box model representative of the shallow-water ocean environment. Numerical simulations demonstrate that the carbonate saturation state of surface waters could significantly decrease and hamper the biogenic production of CaCO3 during the twenty-first century. Similarly, the average saturation state of marine pore waters could decline significantly, inducing dissolution of metastable carbonate phases within the pore-water-sediment system. Such dissolution could buffer the carbon chemistry of the pore waters, but overlying surface waters of reefs and other shallow-water carbonate environments will not accumulate sufficient alkalinity to buffer pH or carbonate saturation state changes owing to invasion of atmospheric CO2.

Page, HN, Courtney TA, DeCarlo EH, Howins NM, Koester I, Andersson AJ.  2019.  Spatiotemporal variability in seawater carbon chemistry for a coral reef flat in Kane'ohe Bay, Hawai'i. Limnology and Oceanography. 64:913-934.   10.1002/lno.11084   AbstractWebsite

Coral reef community composition and ecosystem function may change in response to anthropogenic ocean acidification. However, the magnitude of acidification on reefs will be modified by natural spatial and temporal variability in seawater CO2 chemistry. Consequently, it is necessary to quantify the ecological, biogeochemical, and physical drivers of this natural variability before making robust predictions of future acidification on reefs. In this study, we measured temporal and spatial physiochemical variability on a reef flat in Kane'ohe Bay, O'ahu, Hawai'i, using autonomous sensors at sites with contrasting benthic communities and by sampling surface seawater CO2 chemistry across the reef flat at different times of the day during June and November. Mean and diurnal temporal variability of seawater CO2 chemistry was more strongly influenced by depth gradients (0.5-10 m) on the reef rather than benthic community composition. Spatial CO2 chemistry gradients across the reef flat reflected the cumulative influence from benthic metabolism, bathymetry, and hydrodynamics. Based on graphical assessment of total alkalinity-dissolved inorganic carbon data, reef metabolism in November was dominated by organic carbon cycling over inorganic carbon cycling, while these processes were closely balanced in June. Overall, this study highlights the strong influence of depth on reef seawater CO2 chemistry variability through its effects on benthic biomass to seawater volume ratio, seawater flow rates, and residence time. Thus, the natural complexity of ecosystems where a combination of ecological and physical factors influence reef chemistry must be considered when predicting ecosystem biogeochemical responses to future anthropogenic changes in seawater CO2 chemistry.

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.

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.

Paulsen, ML, Andersson AJ, Aluwihare L, Cyronak T, D'Angelo S, Davidson C, Elwany H, Giddings SN, Page HN, Porrachia M, Schroeter S.  2018.  Temporal changes in seawater carbonate chemistry and carbon export from a Southern California estuary. Estuaries and Coasts. 41:1050-1068.   10.1007/s12237-017-0345-8   AbstractWebsite

Estuaries are important subcomponents of the coastal ocean, but knowledge about the temporal and spatial variability of their carbonate chemistry, as well as their contribution to coastal and global carbon fluxes, are limited. In the present study, we measured the temporal and spatial variability of biogeochemical parameters in a saltmarsh estuary in Southern California, the San Dieguito Lagoon (SDL). We also estimated the flux of dissolved inorganic carbon (DIC) and total organic carbon (TOC) to the adjacent coastal ocean over diel and seasonal timescales. The combined net flux of DIC and TOC (FDIC + TOC) to the ocean during outgoing tides ranged from - 1.8 +/- 0.5 x 10(3) to 9.5 +/- 0.7 x 10(3) mol C h(-1) during baseline conditions. Based on these fluxes, a rough estimate of the net annual export of DIC and TOC totaled 10 +/- 4 x 10(6) mol C year(-1). Following a major rain event (36 mm rain in 3 days), FDIC + TOC increased and reached values as high as 29.0 +/- 0.7 x 10(3) mol C h(-1). Assuming a hypothetical scenario of three similar storm events in a year, our annual net flux estimate more than doubled to 25 +/- 4 x 10(6) mol C year(-1). These findings highlight the importance of assessing coastal carbon fluxes on different timescales and incorporating event scale variations in these assessments. Furthermore, for most of the observations elevated levels of total alkalinity (TA) and pH were observed at the estuary mouth relative to the coastal ocean. This suggests that SDL partly buffers against acidification of adjacent coastal surface waters, although the spatial extent of this buffering is likely small.

Smith, SR, Sarkis S, Murdoch TJT, Weil EA, Croquer A, Bates NR, Johnson RJ, de Putron S, Andersson AJ.  2013.  Threats to coral reefs of Bermuda. Coral reefs of the United Kingdom overseas territories, Coral Reefs of the World. Vol. 4( Sheppard CRC, Ed.)., Dordrecht: Springer Science + Business Media   10.1007/978-94-007-5965-7_13  
Andersson, AJ, Kline DI, Edmunds PJ, Archer SD, Bednaršek N, Carpenter RC, Chadsey M, Goldstein P, Grottoli AG, Hurst TP, King AL, Kübler JE, Kuffner IB, Mackey KRM, Paytan A, Menge B, Riebesell U, Schnetzer A, Warner ME, Zimmerman RC.  2015.  Understanding ocean acidification impacts on organismal to ecological scales. Oceanography magazine. 28:10-21.
Hopner, F, Bender FAM, Ekman AML, Praveen PS, Bosch C, Ogren JA, Andersson A, Gustafsson O, Ramanathan V.  2016.  Vertical profiles of optical and microphysical particle properties above the northern Indian Ocean during CARDEX 2012. Atmospheric Chemistry and Physics. 16:1045-1064.   10.5194/acp-16-1045-2016   AbstractWebsite

A detailed analysis of optical and microphysical properties of aerosol particles during the dry winter monsoon season above the northern Indian Ocean is presented. The Cloud Aerosol Radiative Forcing Experiment (CARDEX), conducted from 16 February to 30 March 2012 at the Maldives Climate Observatory on Hanimaadhoo island (MCOH) in the Republic of the Maldives, used autonomous unmanned aerial vehicles (AUAV) to perform vertical in situ measurements of particle number concentration, particle number size distribution as well as particle absorption coefficients. These measurements were used together with surface-based Mini Micro Pulse Lidar (MiniMPL) observations and aerosol in situ and off-line measurements to investigate the vertical distribution of aerosol particles. Air masses were mainly advected over the Indian subcontinent and the Arabian Peninsula. The mean surface aerosol number concentration was 1717 +/- 604cm(-3) and the highest values were found in air masses from the Bay of Bengal and Indo-Gangetic Plain (2247 +/- 370cm(-3)). Investigations of the free tropospheric air showed that elevated aerosol layers with up to 3 times higher aerosol number concentrations than at the surface occurred mainly during periods with air masses originating from the Bay of Bengal and the Indo-Gangetic Plain. This feature is different compared to what was observed during the Indian Ocean Experiment (INDOEX) conducted in winter 1999, where aerosol number concentrations generally decreased with height. In contrast, lower particle absorption at the surface (sigma(abs)(520nm) = 8.5 + 4.2Wm(-1)) was found during CARDEX compared to INDOEX 1999. Layers with source region specific single-scattering albedo (SSA) values were derived by combining vertical in situ particle absorption coefficients and scattering coefficients calculated with Mie theory. These SSA layers were utilized to calculate vertical particle absorption profiles from MiniMPL profiles. SSA surface values for 550 nm for dry conditions were found to be 0 : 94 +/- 0 : 02 and 0 : 91 +/- 0 : 02 for air masses from the Arabian Sea (and Middle East countries) and India (and Bay of Bengal), respectively. Lidar-derived particle absorption coefficient profiles showed both a similar magnitude and structure as the in situ profiles measured with the AUAV. However, primarily due to insufficient accuracy in the SSA estimates, the lidar-derived absorption coefficient profiles have large uncertainties and are generally weakly correlated to vertically in situ measured particle absorption coefficients. Furthermore, the mass absorption efficiency (MAE) for the northern Indian Ocean during the dry monsoon season was calculated to determine equivalent black carbon (EBC) concentrations from particle absorption coefficient measurements. A mean MAE of 11.6 and 6.9m(2) g(-1) for 520 and 880 nm, respectively, was found, likely representing internally mixed BC containing particles. Lower MAE values for 880 and 520 nm were found for air masses originating from dust regions such as the Arabian Peninsula and western Asia (MAE(880 nm) = 5.6m(2) g(-1), MAE(520 nm) = 9.5m(2) g(-1)) or from closer source regions as southern India (MAE(880 nm) = 4.3m(2) g(-1), MAE(520 nm) = 7. 3m(2) g(-1)).