Spatiotemporal variability and long-term trends of ocean acidification in the California Current System

Due to seasonal upwelling, the upper ocean waters of the California Current System (CCS) have a naturally low pH and aragonite saturation state (Ω arag ), making this region particularly prone to the effects of ocean acidification. Here, we use the Regional Oceanic Modeling System (ROMS) to conduct preindustrial and transient (1995–2050) simulations of ocean biogeochemistry in the CCS. The transient simulations were forced with increasing atmospheric p CO 2 and increasing oceanic dissolved inorganic carbon concentrations at the lateral boundaries, as projected by the NCAR CSM 1.4 model for the IPCC SRES A2 scenario. Our results show a large seasonal variability in pH (range of ~ 0.14) and Ω arag (~ 0.2) for the nearshore areas (50 km from shore). This variability is created by the interplay of physical and biogeochemical processes. Despite this large variability, we find that present-day pH and Ω arag have already moved outside of their simulated preindustrial variability envelopes (defined by ±1 temporal standard deviation) due to the rapidly increasing concentrations of atmospheric CO 2 . The nearshore surface pH of the northern and central CCS are simulated to move outside of their present-day variability envelopes by the mid-2040s and late 2030s, respectively. This transition may occur even earlier for nearshore surface Ω arag , which is projected to depart from its present-day variability envelope by the early- to mid-2030s. The aragonite saturation horizon of the central CCS is projected to shoal into the upper 75 m within the next 25 yr, causing near-permanent undersaturation in subsurface waters. Due to the model's overestimation of Ω arag , this transition may occur even earlier than simulated by the model. Overall, our study shows that the CCS joins the Arctic and Southern oceans as one of only a few known ocean regions presently approaching the dual threshold of widespread and near-permanent undersaturation with respect to aragonite and a departure from its variability envelope. In these regions, organisms may be forced to rapidly adjust to conditions that are both inherently chemically challenging and also substantially different from past conditions.

[1]  N. Gruber,et al.  Variability and trends of ocean acidification in the Southern California Current System: A time series from Santa Monica Bay , 2013 .

[2]  Michael D. DeGrandpre,et al.  Aragonite saturation state dynamics in a coastal upwelling zone , 2013 .

[3]  G. Plattner,et al.  Rapid Progression of Ocean Acidification in the California Current System , 2012, Science.

[4]  S. Doney,et al.  Nutrition and income from molluscs today imply vulnerability to ocean acidification tomorrow , 2012 .

[5]  Ralf Goericke,et al.  Robust empirical relationships for estimating the carbonate system in the southern California Current System and application to CalCOFI hydrographic cruise data (2005–2011) , 2012 .

[6]  Nicholas R. Bates,et al.  Detecting regional anthropogenic trends in ocean acidification against natural variability , 2012 .

[7]  U. Send,et al.  Amplification of hypoxic and acidic events by La Niña conditions on the continental shelf off California , 2011 .

[8]  James C. McWilliams,et al.  Eddy-induced reduction of biological production in eastern boundary upwelling systems , 2011 .

[9]  Nicolas Gruber,et al.  What controls biological production in coastal upwelling systems? Insights from a comparative modeling study , 2011 .

[10]  W. J. Jenkins,et al.  Modeling Methods for Marine Science , 2011 .

[11]  N. Bond,et al.  Climate forcing and the California Current ecosystem , 2011 .

[12]  Nicolas Gruber,et al.  Warming up, turning sour, losing breath: ocean biogeochemistry under global change , 2011, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[13]  S. McClatchie,et al.  Oxygen in the Southern California Bight: Multidecadal trends and implications for demersal fisheries , 2010 .

[14]  J. Largier,et al.  Observations of increased wind‐driven coastal upwelling off central California , 2010 .

[15]  L. Levin,et al.  Ocean oxygen minima expansions and their biological impacts , 2010 .

[16]  G. Plattner.  Ocean acidification in the California Current System , 2009 .

[17]  R. Feely,et al.  A novel method for determination of aragonite saturation state on the continental shelf of central Oregon using multi‐parameter relationships with hydrographic data , 2009 .

[18]  Martijn Gough.  Climate change , 2009, Canadian Medical Association Journal.

[19]  J. Gattuso,et al.  Response of Mediterranean coralline algae to ocean acidification and elevated temperature , 2009 .

[20]  F. Joos,et al.  Imminent ocean acidification in the Arctic projected with the NCAR global coupled carbon cycle-climate model , 2009 .

[21]  F. Chavez,et al.  Diurnal carbon cycling in the surface ocean and lower atmosphere of Santa Monica Bay, California , 2009 .

[22]  F. Joos,et al.  Natural variability and anthropogenic trends in oceanic oxygen in a coupled carbon cycle–climate model ensemble , 2009 .

[23]  E. Maier‐Reimer,et al.  Early detection of ocean acidification effects on marine calcification , 2009 .

[24]  Richard J. Matear,et al.  Southern Ocean acidification: A tipping point at 450-ppm atmospheric CO2 , 2008, Proceedings of the National Academy of Sciences.

[25]  Dudley B. Chelton,et al.  A Global Climatology of Surface Wind and Wind Stress Fields from Eight Years of QuikSCAT Scatterometer Data , 2008 .

[26]  F. Chavez,et al.  Oxygen declines and the shoaling of the hypoxic boundary in the California Current , 2008 .

[27]  R. Feely,et al.  Evidence for Upwelling of Corrosive "Acidified" Water onto the Continental Shelf , 2008, Science.

[28]  J. Sprintall,et al.  Expanding Oxygen-Minimum Zones in the Tropical Oceans , 2008, Science.

[29]  Toby Tyrrell,et al.  Phytoplankton Calcification in a High-CO2 World , 2008, Science.

[30]  Richard A. Feely,et al.  Global relationships of total alkalinity with salinity and temperature in surface waters of the world's oceans , 2006 .

[31]  James C. McWilliams,et al.  Eddy-resolving simulation of plankton ecosystem dynamics in the California Current System , 2006 .

[32]  Ulf Riebesell,et al.  Species‐specific responses of calcifying algae to changing seawater carbonate chemistry , 2006 .

[33]  R. Feely,et al.  Decadal change of the surface water pCO2 in the North Pacific: A synthesis of 35 years of observations , 2006 .

[34]  J. Dunne,et al.  Diagnosing the contribution of phytoplankton functional groups to the production and export of particulate organic carbon, CaCO3, and opal from global nutrient and alkalinity distributions , 2006 .

[35]  E. Maier‐Reimer,et al.  Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms , 2005, Nature.

[36]  Taro Takahashi,et al.  Atmospheric CO2 uptake by a coastal upwelling system , 2005 .

[37]  Richard A. Feely,et al.  A global ocean carbon climatology: Results from Global Data Analysis Project (GLODAP) , 2004 .

[38]  Richard A. Feely,et al.  Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans , 2004, Science.

[39]  Nicolas Gruber,et al.  The Oceanic Sink for Anthropogenic CO2 , 2004, Science.

[40]  James C. McWilliams,et al.  Upwelling response to coastal wind profiles , 2004 .

[41]  James C. McWilliams,et al.  Equilibrium structure and dynamics of the California Current System , 2003 .

[42]  R. Slater,et al.  A new estimate of the CaCO3 to organic carbon export ratio , 2002 .

[43]  Kenneth R. Hinga,et al.  Effects of pH on coastal marine phytoplankton , 2002 .

[44]  K. Taylor.  Summarizing multiple aspects of model performance in a single diagram , 2001 .

[45]  Alexei G. Sankovski,et al.  Special report on emissions scenarios : a special report of Working group III of the Intergovernmental Panel on Climate Change , 2000 .

[46]  Ulf Riebesell,et al.  Reduced calcification of marine plankton in response to increased atmospheric CO2 , 2000, Nature.

[47]  C. Dorman,et al.  Buoy observations of the atmosphere along the west coast of the United States , 1995 .

[48]  Patrick Marchesiello,et al.  Thermal forcing for a global ocean circulation model using a three-year climatology of ECMWF analyses , 1995 .

[49]  F. Millero.  Thermodynamics of the carbon dioxide system in the oceans , 1995 .

[50]  R. Wanninkhof.  Relationship between wind speed and gas exchange over the ocean , 1992 .

[51]  A. Dickson.  Thermodynamics of the dissociation of boric acid in synthetic seawater from 273.15 to 318.15 K , 1990 .

[52]  F. Millero,et al.  A comparison of the equilibrium constants for the dissociation of carbonic acid in seawater media , 1987 .

[53]  A. Mucci.  The solubility of calcite and aragonite in seawater at various salinities , 1983 .

[54]  A. Dickson.  An exact definition of total alkalinity and a procedure for the estimation of alkalinity and total inorganic carbon from titration data , 1981 .

[55]  C. Culberson,et al.  MEASUREMENT OF THE APPARENT DISSOCIATION CONSTANTS OF CARBONIC ACID IN SEAWATER AT ATMOSPHERIC PRESSURE1 , 1973 .

[56]  Ulf Riebesell,et al.  Ocean acidification: The other CO2 problem , 2014 .

[57]  Nancy Knowlton,et al.  Climate change impacts on marine ecosystems. , 2012, Annual review of marine science.

[58]  J. C. Blackford,et al.  pH variability and CO2 induced acidification in the North Sea , 2007 .

[59]  Denis Allemand,et al.  Impacts of ocean acidification on coral reefs and other marine calcifiers : a guide for future research , 2006 .

[60]  Alexander F. Shchepetkin,et al.  The regional oceanic modeling system (ROMS): a split-explicit, free-surface, topography-following-coordinate oceanic model , 2005 .

[61]  F. A. Richards,et al.  The influence of organisms on the composition of sea-water , 1963 .