Variability of alkalinity and the alkalinity‐salinity relationship in the tropical and subtropical surface ocean

Abstract

The variability of total alkalinity (TA) and its relationship with salinity in the tropical and subtropical surface ocean were examined using data collected in various marine environments from a ship of opportunity. In the open ocean regions of the Atlantic, Pacific, and Indian Oceans, sea surface TA variability was observed to be mainly controlled by the simple dilution or concentration (SDC) effect of precipitation and evaporation, and the measured concentrations of TA agreed well with those predicted from salinity and temperature. Non-SDC changes in alkalinity in ocean margins and inland seas were examined by comparing the salinity-normalized alkalinity with that of the open ocean end-member. Non-SDC alkalinity additions to the western North Atlantic margin, eastern North Pacific margin, and Mediterranean Sea were identified, which mainly resulted from river inputs and shelf currents. In contrast, removal of TA through formation and sedimentation of calcium carbonate was observed to be an important control in the Red Sea. The concentration of the river end-member can only be reliably derived from the y intercept of TA-S regression (TA S0 ) in river-dominated systems such as estuaries and river plumes. In coastal regions where other processes (evaporation, shelf currents, upwelling, calcification, etc.) are more influential, TA S0 can significantly deviate from the river water concentration and hence be an unreliable indicator of it. Negative values of TA S0 can result from non-SDC TA removal at the low salinity end (relative to the salinity of the oceanic end-member) and/or non-SDC TA addition at high salinities (as occurs in the Mediterranean Sea).

Climatological variations of total alkalinity and total dissolved inorganic carbon in the Mediterranean Sea surface waters

“…In the Mediterranean Sea, several studies have shown that the relationship between A T and S is linear (Copin-Montégut, 1993;Copin-Montégut and Bégovic, 2002;Hassoun et al, 2015b;Jiang et al, 2014;Rivaro et al, 2010;. In other studies, the sea surface temperature (T ) has been included as an additional proxy for changes in surface water A T related to convective mixing (Lee et al, 2006;Touratier and Goyet, 2011).…”

Estimating total alkalinity for coastal ocean acidification monitoring at regional to continental scales in Australian coastal waters

“…Waters with higher TA are less prone to rapid change in ocean pH and may provide refuge for marine biodiversity in the face of OA. TA is conservatively related to salinity due to convective mixing and the addition or removal of freshwater to a water 30 mass (Cai et al, 2010;Jiang et al, 2014;Lee et al, 2006;Millero et al, 1998). This relationship has been exploited to predict alkalinity at the global scale from historical databases of ocean salinity (Lee et al, 2006;Millero et al, 1998).…”

“…To address this limitation, additional proxy variables have been incorporated into predictive alkalinity models to account for processes that affect TA non-conservatively (Jiang et al, 2014). For example, seawater temperature 40…”

“…has been used to help account for mixing between water masses (Jiang et al, 2014;Lee et al, 2006) and associated nutrient changes. To account for primary production, chlorophyll-a (CHL) (Hales et al, 2012), dissolved oxygen or nitrate (N) have featured in such models (Bostock et al, 2013;Brewer and Goldman, 1976;Lee et al, 2008).…”

“…Indeed, the seasonality in the residuals was seen to co-vary with seasonal freshening in salinity data (SF2). All of these processes affect TA signals directly, so a clear signal may be seen in the data (Brewer and Goldman, 1976;Cai et al, 2010;Jiang et al, 2014;Shadwick et al, 2011), but cannot be monitored via remote sensing (or BM3). In fact, when N was 40…”