Despite recent interest in understanding long-term trends in ocean acidity, natural variations of carbon chemistry on short timescales are still poorly understood. Unfortunately, historical observations of the oceanic CO2 system are relatively few in number. Such data are particularly scarce along the highly productive Canadian Pacific coast. However, hydrographic data such as temperature, salinity, oxygen and nutrients have been collected regularly in this region. I developed a fully cross-validated statistical model to predict the aragonite saturation state (Ωarag), a biologically relevant measure of the carbonate system. Different sensitivity tests were performed to assess the robustness of the statistical modelling skill to different model structures. In particular, this study found that in situ temperature and O2 used together were strong predictors of Ωarag. The carbon data used to build this statistical model came from five hydrographic surveys along the Pacific coast of Canada (in July 1998, August 2004, late May 2007, February 2010 and early August 2010) that contain direct measurements of CO2 system parameters. Only data from a depth range of 0-750 m were used, as data from below 750 m showed biases due to calcium carbonate dissolution. Although processes such as solar warming and gas exchange occur in the surface and could possibly introduce biases in the model, I show that these surface data can be included. The ability of the statistical models to compute robust estimates of Ωarag was assessed by exploring the generalizability of the model through cross-validation procedures using different partitions of the data. By predicting lnΩarag rather than Ωarag directly, I obtained a strong and robust predictive relationship. This MLR model form yielded a high value in the squared correlation coefficient between predicted and observed values (0.96) and a low percentage in erroneous prediction of undersaturated conditions (3.1%). This relationship was found to be insensitive to changes in spatial domain or interannual variability in the data. These results suggest that the model can be used to estimate the distribution of Ωarag along the outer west coast of Canada when basic hydrographic data on temperature and O2 are available. Predictions of Ωarag from historical observations (1980-2009) in this region reveal that the saturation horizon (Ωarag=1) tended to be more stable in winter and spring and highly variable and occasionally shallow in summer and fall during and following the upwelling season. Undersaturation with respect to aragonite was more likely to occur at shallower depths over the shelf relative to adjacent offshore waters likely as a result of upwelling. The Ωarag saturation horizon tended to be more variable in depth on the shelf compared to offshore waters. The saturation horizon tended to occur at deeper depths over the Queen Charlotte Sound (QCS) shelf and be more stable with respect to the west coast of Vancouver island (WCVI). Thus, the WCVI may experience adverse effects of ocean acidification more acutely than QCS. The use of this approach may provide insight into natural variability and the key controls of Ωarag in future studies at a low cost. However, this predictive model cannot hind-cast data to evaluate the presence of the anthropogenic signal. / Graduate

Deep-water or cold-water corals are abundant and highly diverse, greatly increase habitat heterogeneity and species richness, thereby forming one of the most significant ecosystems in the deep sea. Despite this remote location, they are not removed from the different anthropogenic disturbances that commonly impact their shallow-water counterparts. The global decrease in seawater pH due to increases in atmospheric CO2 are changing the chemical properties of the seawater, decreasing the concentration of carbonate ions that are important elements for different physiological and ecological processes. Predictive models forecast a shoaling of the carbonate saturation in the water column due to OA, and suggest that cold-water corals are at high risk, since large areas of suitable habitat will experience suboptimal conditions by the end of the century. The main objective of this study was to explore the fate of the deep-water coral community in time of environmental change. To better understand the impact of climate change this study focused in two of the most important elements of deep-sea coral habitat, the reef forming coral Lophelia pertusa and the octocoral community, particularly the gorgonian Callogorgia delta. By means of controlled experiments, I examined the effects of long- and short-term exposures to seawater simulating future scenarios of ocean acidification on calcification and feeding efficiency. Finally In order to understand how the environment influences the community assembly, and ultimately how species cope with particular ecological filters, I integrated different aspects of biology such functional diversity and ecology into a more evolutionary context in the face of changing environment. My results suggest that I) deep-water corals responds negatively to future OA by lowering the calcification rates, II) not all individuals respond in the same way to OA with high intra-specific variability providing a potential for adaptation in the long-term III) there is a disruption in the balance between accretion and dissolution that in the long term can shift from net accretion to net dissolution, and IV) there is an evolutionary implication for certain morphological features in the coral community that can give an advantage under stresfull conditions. Nevertheless, the suboptimal conditions that deep-water corals will experience by the end of the century could potentially threaten their persistence, with potentially negative consequences for the future stability of this already fragile ecosystem. / Biology

Ocean uptake of anthropogenic CO2 causes ocean acidification, a secular, global-scale decline in the pH of seawater. In order to better understand the implications of contemporary acidification for marine organisms and ecosystems, there is a need to better characterise natural variability in carbonate chemistry. In this thesis, climatological seasonal variability of sea surface pH and aragonite saturation state (OmegaA) in the open ocean is indirectly derived from other parameters of the marine CO2 system, namely total alkalinity (TA) and seawater pCO2/fCO2 (pCO2sw/fCO2sw). New monthly sea surface TA, fCO2sw and temperature climatologies are developed for this purpose, utilising newly-released observational synthesis products (PACIFICA for TA and SOCAT v2 for fCO2sw). Two versions of the new SST climatology are developed, referred to as upper and lower SST (USST and LSST), to test sensitivity to the depth range of the input observations. Annual ranges are generally found to be larger for the USST climatology, derived using observations from the upper 2 m, compared to LSST (which is based on deeper observations). Further, a seasonal cycle is found in the monthly average of the differences between these climatologies north of 30 degN, perhaps partly due to seasonal variation in near-surface stratification. The USST seasonal ranges are also found to be generally larger than in two previous SST climatologies, however, difference in the depth distribution of the input measurements is unlikely the main cause. The new monthly sea surface TA climatology extends coverage into the Nordic seas, excluded from previous climatologies. TA seasonality is found to be small outside of regions with large seasonal ranges in salinity. Large seasonal ranges in salinity and TA are found beneath the Intertropical Convergence Zone, in the Antarctic seasonal sea ice zone and in the western Greenland Sea. Non-salinity driven TA seasonality is found to be large in the Gulf of Alaska, eastern equatorial Pacific and western Greenland Sea. Compared to the Lee et al. (2006) TA climatology, substantially lower annual means and seasonal ranges are found for the subarctic Pacific, a region with greatly improved coverage courtesy of PACIFICA. The pH/OmegaA climatologies derived in the final chapter suggest pH seasonality is predominantly temperature driven in the subtropics and mainly driven by variation in salinity normalised dissolved inorganic carbon (sDIC) in the subpolar north Atlantic, western subarctic Pacific and Southern Ocean. Salinity variation is found to only exert a strong influence on pH seasonality in the western Greenland Sea. Climatological seasonal pH ranges are found to be mostly small in the tropics (<0.05), moderate in the subtropics (0.05-0.10) but very large (>0.1) in parts of the Ross, Weddell, Irminger and Iceland Seas and western subarctic Pacific gyre. OmegaA seasonality is found to be predominantly sDIC-driven everywhere except in the western Greenland Sea, with temperature variation generally being of modest influence. Seasonal cycles of pH and OmegaA are found to be in anti-phase where pH is mainly thermally driven and in-phase where pH is mainly sDIC-forced (both pH and OmegaA vary inversely with DIC). Comparison is made between the primary new pH/OmegaA climatology and various open ocean carbonate chemistry time-series. The climatology captures the general form of the climatological seasonal cycles of pH and OmegaA from the time-series, although with some differences in phasing and seasonal range. Analysing the time-series for long-term trends, I find that inter-decadal anthropogenic CO2 uptake driven pH and OmegaA declines can be modulated by trends in temperature, salinity or sTA. Investigation is also conducted into how the amplitude of pH and OmegaA seasonal cycles might change by 2100 for a subpolar and subtropical time-series. Under a high CO2 emissions scenario, the seasonal range of pH is found to be strongly enhanced for the subpolar time-series and moderately reduced for the subtropical time-series, with both being due to changes in seawater buffer capacity. / Graduate / 0425 / 0415 / robdj87@hotmail.com