Spatio-temporal survey of the coastal carbonate system offshore Lebanon-Levantine Mediterranean Sea

2020 ◽  
Author(s):  
Abed El Rahman Hassoun ◽  
Milad Fakhri ◽  
Majd Habib ◽  
Anthony Ouba ◽  
Sharif Jemaa ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Dissolved Inorganic Carbon ◽  
Eastern Mediterranean ◽  
Mixed Layer Depth ◽  
Total Alkalinity ◽  
Critical Parameters ◽  
Carbonate System ◽  
Preliminary Results ◽  
Open Sea ◽  
Spatio Temporal

<p>The coastal carbonate system regulates the pH of the coastal waters and controls the circulation of CO<sub>2</sub> between land-sea interfaces and open sea system. In the context of the ELME (Evaluation of the Lebanese Marine Environment: A multidisciplinary study) project, a seasonal survey of the carbonate system has been started in 2019 through the sampling of 3 different transects starting from the coast towards the open sea, offshore two Lebanese cities (Beirut and Tyre) to evaluate the spatio-temporal variations of this system in coastal areas. The carbonate chemistry is being studied by measuring both total alkalinity (A<sub>T</sub>) and total dissolved inorganic carbon (C<sub>T</sub>), together with other critical parameters in coastal ecosystems such as temperature, salinity, pH, dissolved oxygen, nutrients (phosphates, nitrates, nitrites, silicates), and chlorophyll a. The preliminary results show that the highest carbonate system inventories (2546.4 and 2266 µmol kg<sup>-1</sup> for A<sub>T</sub> and C<sub>T</sub> respectively) were measured in transects influenced by discharges of dumpsite and port areas (offshore Beirut) where positive and significant correlations (p << 0.005) have been recorded with nutrients, particularly with nitrites (> 10 µmol kg<sup>-1</sup>). Furthermore, TrOCA approach was used to estimate the anthropogenic CO<sub>2</sub> concentrations (C<sub>ANT</sub>) below the mixed layer depth. The results demonstrate that all waters in both studied areas are contaminated by C<sub>ANT</sub>, even the deep ones (> 400 m) located in the furthest monitored station, with values greater than 70 µmol kg<sup>-1</sup>. This fact raises concerns about the effects of such relatively high C<sub>ANT</sub> concentrations on coastal organisms therein. This work presents the preliminary results of an ongoing study. The continuity of this project will help to assess the relationship between land-based anthropogenic pressures and the coastal biogeochemistry in a changing Eastern Mediterranean Sea.</p>

scholarly journals Distributions of the carbonate system properties, anthropogenic CO<sub>2</sub>, and acidification during the 2008 BOUM cruise (Mediterranean Sea)

2012 ◽  
Vol 9 (3) ◽  
pp. 2709-2753 ◽  
Author(s):  
F. Touratier ◽  
V. Guglielmi ◽  
C. Goyet ◽  
L. Prieur ◽  
M. Pujo-Pay ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Dissolved Inorganic Carbon ◽  
Marine Ecosystem ◽  
Total Alkalinity ◽  
Carbonate System ◽  
Simple Method ◽  
Deep Waters ◽  
History Of ◽  
The Mediterranean ◽  
System Properties

Abstract. We relate here the distributions of two carbonate system key properties (total alkalinity, AT; and total dissolved inorganic carbon, CT) measured along a section in the Mediterranean Sea, going from Marseille (France) to the south of the Cyprus Island, during the 2008 BOUM cruise. The three main objectives of the present study are (1) to draw and comment on the distributions of AT and CT in the light of others properties like salinity, temperature, and dissolved oxygen, (2) to estimate the distribution of the anthropogenic CO2 (CANT) in the intermediate and the deep waters, and (3) to calculate the resulting variation of pH (acidification) since the beginning of the industrial era. Since the calculation of CANT is always an intense subject of debate, we apply two radically different approaches to estimate CANT: the very simple method TrOCA and the MIX approach, the latter being more precise but also more difficult to apply. A clear picture for the AT and the CT distributions is obtained: the mean concentration of AT is higher in the oriental basin while that of CT is higher in the occidental basin of the Mediterranean Sea, fully coherent with the previous published works. Despite of the two very different approaches we use here (TrOCA and MIX), the estimated distributions of CANT are very similar. These distributions show that the minimum of CANT encountered during the BOUM cruise is higher than 46.3 μmol kg−1 (TrOCA) or 48.8 μmol kg−1(MIX). All Mediterranean water masses (even the deepest) appear to be highly contaminated by CANT, as a result of the very intense advective processes that characterize the recent history of the Mediterranean circulation. As a consequence, unprecedented levels of acidification are reached with an estimated decrease of pH since the pre-industrial era of −0.148 to −0.061 pH unit, which places the Mediterranean Sea as one of the most acidified world marine ecosystem.

New insights into nutrients dynamics and the carbonate system using a neural network approach in the Mediterranean Sea

2020 ◽  
Author(s):  
Marine Fourrier ◽  
Laurent Coppola ◽  
Fabrizio D'Ortenzio
Keyword(s):  
Neural Network ◽  
Mediterranean Sea ◽  
Dissolved Inorganic Carbon ◽  
In Situ Measurements ◽  
Total Alkalinity ◽  
Anthropogenic Pressure ◽  
Carbonate System ◽  
The Mediterranean ◽  
The Impact

&lt;p&gt;The semi-enclosed nature of the Mediterranean Sea, together with its small inertia which is due to the relatively short residence time of its water masses, make it highly reactive to external forcings and anthropogenic pressure. In this context, several rapid changes have been observed in physical and biogeochemical processes in recent decades, partly masked by episodic events and high regional variability. To better understand the underlying processes driving the Mediterranean evolution and, anticipate changes, the measurement, and integration of many biogeochemical variables are mandatory.&lt;/p&gt;&lt;p&gt;The development of new BGC sensors implemented on &lt;em&gt;in situ&lt;/em&gt; autonomous platforms allows to increase the acquisition of essential biogeochemical variables. However, the measurements carried out by&lt;em&gt; in situ&lt;/em&gt; autonomous platforms (e.g. profiling floats, gliders, moorings) are not exhaustive.&lt;/p&gt;&lt;p&gt;Recently, deep learning techniques and in particular neural networks have been developed. The CANYON-MED (for Carbonate system and Nutrients concentration from hYdrological properties and Oxygen using a Neural-network in the MEDiterranean Sea) neural network-based method provides estimations of nutrients (i.e. nitrates, phosphates, and silicates) and carbonate system variables (i.e. total alkalinity, dissolved inorganic carbon, pH&lt;sub&gt;T&lt;/sub&gt;) from systematically measured oceanographic variables such as in situ measurements of pressure, temperature, salinity, and oxygen together with geolocation and date of sampling.&lt;/p&gt;&lt;p&gt;This regional approach, therefore, using quality-controlled in situ measurements from more than 35 cruises. CANYON-MED obtains satisfactory results: accuracies of 0.73, 0.045, and 0.70 &amp;#181;mol.kg&lt;sup&gt;-1&lt;/sup&gt; for the nitrates, phosphates and silicates concentrations respectively, and 0.016, 11 &amp;#181;mol.kg&lt;sup&gt;-1&lt;/sup&gt; and 10 &amp;#181;mol.kg&lt;sup&gt;-1&lt;/sup&gt; for pH&lt;sub&gt;T&lt;/sub&gt;, total alkalinity and dissolved organic carbon respectively. CANYON-MED thus generates &amp;#8220;virtual&amp;#8221; data of parameters not yet measured by autonomous platforms, while ably reproducing the data already sampled, emphasizing its ability to fill the gaps in time-series.&lt;/p&gt;&lt;p&gt;Hence, by applying it to the large and growing network of autonomous platforms in the Mediterranean Sea, this method allows us to gain new insights into nutrients and carbonate system dynamics in targeted areas. In particular, in the northwestern Mediterranean Sea, the impact of deep convection on biogeochemistry (e.g., nutrient replenishment and pH&lt;sub&gt;T&lt;/sub&gt; variability) is highly variable over time and poorly covered by observing networks. In this case, CANYON-MED would improve our observations and understanding of the dynamic and coupled system.&lt;/p&gt;

scholarly journals The CO<sub>2</sub> system in the Mediterranean Sea: a basin wide perspective

Ocean Science ◽  
2014 ◽  
Vol 10 (1) ◽  
pp. 69-92 ◽  
Author(s):  
M. Álvarez ◽  
H. Sanleón-Bartolomé ◽  
T. Tanhua ◽  
L. Mintrop ◽  
A. Luchetta ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Dissolved Inorganic Carbon ◽  
Eastern Mediterranean ◽  
Total Alkalinity ◽  
Time Variability ◽  
Base Line ◽  
Wide Perspective ◽  
The Mediterranean ◽  
System Variables ◽  
East West

Abstract. The Mediterranean Sea (MedSea) is considered a "laboratory basin" being an ocean in miniature, suffering dramatic changes in its oceanographic and biogeochemical conditions derived from natural and anthropogenic forces. Moreover, the MedSea is prone to absorb and store anthropogenic carbon due to the particular CO2 chemistry and the active overturning circulation. Despite this, water column CO2 measurements covering the whole basin are scarce. This work aims to be a base-line for future studies about the CO2 system space-time variability in the MedSea combining historic and modern CO2 cruises in the whole area. Here we provide an extensive vertical and longitudinal description of the CO2 system variables (total alkalinity – TA, dissolved inorganic carbon – DIC and pH) along an East-West transect and across the Sardinia-Sicily passage in the MedSea from two oceanographic cruises conducted in 2011 measuring CO2 variables in a coordinated fashion, the RV Meteor M84/3 and the RV Urania EuroFleets 11, respectively. In this sense, we provide full-depth and length CO2 distributions across the MedSea, and property-property plots showing in each sub-basin post-Eastern Mediterranean Transient (EMT) situation with regard to TA, DIC and pH. The over-determined CO2 system in 2011 allowed performing the first internal consistency analysis for the particularly warm, high salinity and alkalinity MedSea waters. The CO2 constants by Mehrbach et al. (1973) refitted by Dickson and Millero (1987) are recommended. The sensitivity of the CO2 system to the atmospheric CO2 increase, DIC and/or TA changes is evaluated by means of the Revelle and buffer factors.

scholarly journals Seasonal and Interannual Variability of the CO2 System in the Eastern Mediterranean Sea: A Case Study in the North Western Levantine Basin

2021 ◽  
Vol 8 ◽  
Author(s):  
Cathy Wimart-Rousseau ◽  
Thibaut Wagener ◽  
Marta Álvarez ◽  
Thierry Moutin ◽  
Marine Fourrier ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Annual Cycle ◽  
Eastern Mediterranean ◽  
Total Alkalinity ◽  
Carbonate System ◽  
Eastern Mediterranean Sea ◽  
The North ◽  
Levantine Basin ◽  
The Future ◽  
North Western

The seasonal variability of the carbonate system in the eastern Mediterranean Sea (EMed) was investigated based on discrete total alkalinity (AT), total dissolved inorganic carbon (CT), and pH measurements collected during three cruises around Crete between June 2018 and March 2019. This study presents a detailed description of this new carbonate chemistry dataset in the eastern Mediterranean Sea. We show that the North Western Levantine Basin (NWLB) is unique in terms of range of AT variation vs. CT variation in the upper water column over an annual cycle. The reasons for this singularity of the NWLB can be explained by the interplay between strong evaporation and the concomitant consumption of CT by autotrophic processes. The high range of AT variations, combined to temperature changes, has a strong impact on the variability of the seawater pCO2 (pCO2SW). Based on Argo float data, an entire annual cycle for pCO2SW in the NWLB has been reconstructed in order to estimate the temporal sequence of the potential “source” and “sink” of atmospheric CO2. By combining this dataset with previous observations in the NWLB, this study shows a significant ocean acidification and a decrease in the oceanic surface pHT25 of −0.0024 ± 0.0004 pHT25 units.a–1. The changes in the carbonate system are driven by the increase of atmospheric CO2 but also by unexplained temporal changes in the surface AT content. If we consider that the EMed will, in the future, encounter longer, more intense and warmer summer seasons, this study proposes some perspectives on the carbonate system functioning of the “future” EMed.

scholarly journals The CO<sub>2</sub> system in the Mediterranean Sea: a basin wide perspective

2013 ◽  
Vol 10 (4) ◽  
pp. 1447-1504 ◽  
Author(s):  
M. Álvarez ◽  
H. Sanleón-Bartolomé ◽  
T. Tanhua ◽  
L. Mintrop ◽  
A. Luchetta ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Dissolved Inorganic Carbon ◽  
Eastern Mediterranean ◽  
Total Alkalinity ◽  
Time Variability ◽  
System Variability ◽  
Wide Perspective ◽  
The Mediterranean ◽  
System Variables ◽  
East West

Abstract. This paper provides an extensive vertical and longitudinal description of the CO2 system variables (Total Alkalinity – TA, dissolved inorganic carbon – DIC and pH) along an East-West transect and across the Sardinia–Sicily passage in the Mediterranean Sea (MedSea) from two oceanographic cruises conducted in 2011 measuring CO2 variables in a coordinated fashion, the RV Meteor M84/3 and the RV Urania EuroFleets 11, respectively. The over-determined CO2 system allowed performing the first internal consistency analysis for the particularly warm, high salinity and alkalinity MedSea waters. This basin is considered a "laboratory basin" suffering dramatic changes in its oceanographic and biogeochemical conditions derived from natural and anthropogenic forces. Despite this, little is known about the CO2 system variability in the whole basin. This work aims to be a benchmark for future studies about the CO2 system space-time variability in the MedSea. In this sense we provide full-depth and length CO2 distributions across the MedSea, and property – property plots showing in each sub-basin post-Eastern Mediterranean Transient (EMT) situation with regard to TA, DIC and pH.

scholarly journals PRELIMINARY STUDIES ON SEDIMENT CORE FROM THE TYRO BASIN

2017 ◽  
Vol 50 (1) ◽  
pp. 324
Author(s):  
M. Geraga ◽  
Ch. Anagnostou ◽  
I. Iliopoulos ◽  
M. Kontali
Keyword(s):  
Mediterranean Sea ◽  
Sediment Core ◽  
Eastern Mediterranean ◽  
Planktonic Foraminifera ◽  
Mineralogical Composition ◽  
Eastern Mediterranean Sea ◽  
Sediment Samples ◽  
Preliminary Results ◽  
The Core ◽  
Mineral Constituents

The present paper summarizes the preliminary results of the mineralogical and micropaleontological analysis conducted on sediment samples from core TYR05 retrieved from the anoxic and hypersaline Tyro basin in the eastern Mediterranean Sea. The core comprises a complex lithostratigraphic sequence attributed to the strong geodynamic regime of the area. The planktonic foraminifera associations present fluctuations which coincide with changes in the lithology of the core. The mineralogical composition of the sediments shows influence from the evaporites developed on the bottom of the basin. The mineral constituents in association to the microfauna assemblages suggest that the sediments include sapropelic layers. Further analyses are needed in order to determine safely the sapropelic deposits.

Organic and inorganic whole system metabolism in two acidified coastal systems in Ireland

2020 ◽  
Author(s):  
Maria Teresa Guerra ◽  
Carlos Rocha
Keyword(s):  
Ocean Acidification ◽  
Dissolved Inorganic Carbon ◽  
Total Alkalinity ◽  
Carbonate System ◽  
Net Community Production ◽  
Coastal Acidification ◽  
Autumn And Winter ◽  
System Metabolism ◽  
Internal Buffer ◽  
Community Production

&lt;p&gt;Organic and inorganic whole system metabolism for two Irish coastal areas were compared to evaluate carbonate system resilience to acidification. The two systems are characterized by contrasting watershed input types and composition. Kinvara Bay is fed by Submarine Groundwater Discharge (SGD) derived from a karstic catchment while Killary Harbour is fed by river discharge draining a siliciclastic catchment. Freshwater sources to sea have distinct Total Alkalinity (TA) and Dissolved Inorganic Carbon (DIC) concentrations, higher and lower than the open ocean, respectively, but both evidence seasonally variable low pH, ranging from 6.20 to 7.50. Retention of TA and DIC was calculated for the two areas using LOICZ methodology. In Kinvara bay, annually averaged retention of DIC was greater than for TA (5 &amp;#215; 10&lt;sup&gt;4&lt;/sup&gt; and 1.5 &amp;#215; 10&lt;sup&gt;5&lt;/sup&gt; mol d&lt;sup&gt;-1&lt;/sup&gt;), suggesting the system is acidifying further. Conversely, Killary Harbour shows negative TA and DIC retention, with DIC:TA &lt;1, suggesting an internal buffer against ocean acidification is operating.&lt;/p&gt;&lt;p&gt;Net Community Production (NCP) was calculated for both systems using Dissolved Oxygen data. Subsequently, we estimated Net Community Calcification (NCC) from the ratio between TA and DIC. NCP was always positive in Killary Harbour with an average of 318 mmol O&lt;sub&gt;2&lt;/sub&gt; m&lt;sup&gt;-2 &lt;/sup&gt;d&lt;sup&gt;-1&lt;/sup&gt; (equivalent to 89 mol C m&lt;sup&gt;-2&lt;/sup&gt; y&lt;sup&gt;-1&lt;/sup&gt;). However, Kinvara Bay shows relatively lower positive NCP in spring and summer (average of 46 mmol O&lt;sub&gt;2&lt;/sub&gt; m&lt;sup&gt;-2&lt;/sup&gt; d&lt;sup&gt;-1&lt;/sup&gt;), but negative NCP in autumn and winter. Therefore, Kinvara Bay&amp;#8217;s Total Organic Carbon (TOC) production was low, at ~21 g m&lt;sup&gt;-2&lt;/sup&gt; y&lt;sup&gt;-1&lt;/sup&gt; and not enough to overcome acidification driven by the SGD source composition. These results emphasize the complexity of interactions between the drivers of coastal acidification rate, affecting our ability to accurately assess the resilience of the carbonate system in these areas to ocean acidification pressure in the future.&lt;/p&gt;

SMOS-based estimation and validation of Total Alkalinity in the Mediterranean basin

2020 ◽  
Author(s):  
Roberto Sabia ◽  
Estrella Olmedo ◽  
Giampiero Cossarini ◽  
Aida Alvera-Azcárate ◽  
Veronica Gonzalez-Gambau ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Mediterranean Sea ◽  
Mediterranean Basin ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Total Alkalinity ◽  
Surface Salinity ◽  
Carbonate System ◽  
The Mediterranean ◽  
The Mediterranean Basin

&lt;p&gt;ESA SMOS satellite [1] has been providing first-ever Sea Surface Salinity (SSS) measurements from space for over a decade now. Until recently, inherent algorithm limitations or external interferences hampered a reliable provision of satellite SSS data in semi-enclosed basin such as the Mediterranean Sea. This has been however overcome through different strategies in the retrieval scheme and data filtering approach [2, 3]. This recent capability has been in turn used to infer the spatial and temporal distribution of Total Alkalinity (TA - a crucial parameter of the marine carbonate system) in the Mediterranean, exploiting basin-specific direct relationships existing between salinity and TA.&lt;/p&gt;&lt;p&gt;Preliminary results [4] focused on the differences existing in several parameterizations [e.g, 5] relating these two variables, and how they vary over a seasonal to interannual timescale.&lt;/p&gt;&lt;p&gt;Currently, to verify the consistency and accuracy of the derived products, these data are being validated against a proper ensemble of in-situ, climatology and model outputs within the Mediterranean basin. An error propagation exercise is also being planned to assess how uncertainties in the satellite data would translate into the final products accuracy.&lt;/p&gt;&lt;p&gt;The resulting preliminary estimates of Alkalinity in the Mediterranean Sea will be linked to the overall carbonate system in the broader context of Ocean Acidification assessment and marine carbon cycle.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;[1] J. Font et al., &quot;SMOS: The Challenging Sea Surface Salinity Measurement From Space,&quot; in Proceedings of the IEEE, vol. 98, no. 5, pp. 649-665, May 2010. doi: 10.1109/JPROC.2009.2033096&lt;/p&gt;&lt;p&gt;[2] Olmedo, E., J. Martinez, A. Turiel, J. Ballabrera-Poy, and M. Portabella,&amp;#160; &amp;#8220;Debiased non-Bayesian retrieval: A novel approach to SMOS Sea Surface Salinity&amp;#8221;. Remote Sensing of Environment 193, 103-126 (2017).&lt;/p&gt;&lt;p&gt;[3] Alvera-Azc&amp;#225;rate, A., A. Barth, G. Parard, J.-M. Beckers, Analysis of SMOS sea surface salinity data using DINEOF, In Remote Sensing of Environment, Volume 180, 2016, Pages 137-145, ISSN 0034-4257, https://doi.org/10.1016/j.rse.2016.02.044.&lt;/p&gt;&lt;p&gt;[4] Sabia, R., E. Olmedo, G. Cossarini, A. Turiel, A. Alvera-Azc&amp;#225;rate, J. Martinez, D. Fern&amp;#225;ndez-Prieto, Satellite-driven preliminary estimates of Total Alkalinity in the Mediterranean basin, Geophysical Research Abstracts, Vol. 21, EGU2019-17605, EGU General Assembly 2019, Vienna, Austria, April 7-12, 2019.&lt;/p&gt;&lt;p&gt;[5] Cossarini, G., Lazzari, P., and Solidoro, C.: Spatiotemporal variability of alkalinity in the Mediterranean Sea, Biogeosciences, 12, 1647-1658, https://doi.org/10.5194/bg-12-1647-2015, 2015.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Decadal changes in surface carbon dioxide and related variables in the Mediterranean Sea as inferred from a coupled data-diagnostic model approach

2009 ◽  
Vol 66 (7) ◽  
pp. 1538-1546 ◽  
Author(s):  
Ferial Louanchi ◽  
Meriem Boudjakdji ◽  
Lamri Nacef
Keyword(s):  
Carbon Dioxide ◽  
Mediterranean Sea ◽  
Dissolved Inorganic Carbon ◽  
Atmospheric Co2 ◽  
Total Alkalinity ◽  
Diagnostic Model ◽  
Surface Carbon ◽  
The Mediterranean ◽  
The 1960S ◽  
Model Approach

Abstract Louanchi, F., Boudjakdji, M, and Nacef, L. 2009. Decadal changes in surface carbon dioxide and related variables in the Mediterranean Sea as inferred from a coupled data-diagnostic model approach. – ICES Journal of Marine Science, 66: 1538–1546. A coupled approach based on available datasets of temperature, salinity, oxygen, nutrients, and chlorophyll, and a surface layer box model previously developed and modified for the present study, allowed us to reconstruct dissolved inorganic carbon (DIC), total alkalinity, and carbon dioxide fugacity (fCO2) mixed-layer fields for the Mediterranean Sea, from the 1960s to the 1990s. The approach used in this study resulted in a 7% relative error on reconstructed surface fCO2 fields. The Mediterranean Sea transformed from a source of 0.62 Tg C year−1 for atmospheric CO2 in the 1960s, to a net sink of −1.98 Tg C year−1 in the 1990s. The annual cycle in surface fCO2 was driven mainly by temperature variations in the Mediterranean Sea, whereas its decadal variations resulted from a balance between primary production and the thermal effect. According to our model results, the atmospheric CO2 increase of ∼40 µatm over the period of our investigation induced an increase in DIC of ∼30 µmol l−1 in surface waters. A 50% reduction in the magnitude of seasonal variations in surface temperature occurred during the 1990s relative to the earlier decades. Therefore, surface fCO2 only increased by 24 µatm from the 1960s to the 1990s. Changes in pH were not significant over this period.

scholarly journals The Sensitivity of the Marine Carbonate System to Regional Ocean Alkalinity Enhancement

2021 ◽  
Vol 3 ◽  
Author(s):  
Daniel J. Burt ◽  
Friederike Fröb ◽  
Tatiana Ilyina
Keyword(s):  
Southern Ocean ◽  
Dissolved Inorganic Carbon ◽  
Ocean Model ◽  
Total Alkalinity ◽  
Surface Pattern ◽  
Carbon Uptake ◽  
Max Planck ◽  
Carbonate System ◽  
Carbon Cycle Model ◽  
Marine Carbonate

Ocean Alkalinity Enhancement (OAE) simultaneously mitigates atmospheric concentrations of CO2 and ocean acidification; however, no previous studies have investigated the response of the non-linear marine carbonate system sensitivity to alkalinity enhancement on regional scales. We hypothesise that regional implementations of OAE can sequester more atmospheric CO2 than a global implementation. To address this, we investigate physical regimes and alkalinity sensitivity as drivers of the carbon-uptake potential response to global and different regional simulations of OAE. In this idealised ocean-only set-up, total alkalinity is enhanced at a rate of 0.25 Pmol a-1 in 75-year simulations using the Max Planck Institute Ocean Model coupled to the HAMburg Ocean Carbon Cycle model with pre-industrial atmospheric forcing. Alkalinity is enhanced globally and in eight regions: the Subpolar and Subtropical Atlantic and Pacific gyres, the Indian Ocean and the Southern Ocean. This study reveals that regional alkalinity enhancement has the capacity to exceed carbon uptake by global OAE. We find that 82–175 Pg more carbon is sequestered into the ocean when alkalinity is enhanced regionally and 156 PgC when enhanced globally, compared with the background-state. The Southern Ocean application is most efficient, sequestering 12% more carbon than the Global experiment despite OAE being applied across a surface area 40 times smaller. For the first time, we find that different carbon-uptake potentials are driven by the surface pattern of total alkalinity redistributed by physical regimes across areas of different carbon-uptake efficiencies. We also show that, while the marine carbonate system becomes less sensitive to alkalinity enhancement in all experiments globally, regional responses to enhanced alkalinity vary depending upon the background concentrations of dissolved inorganic carbon and total alkalinity. Furthermore, the Subpolar North Atlantic displays a previously unexpected alkalinity sensitivity increase in response to high total alkalinity concentrations.

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