Effects of upwelling increase on ocean acidification in the California and Canary Current systems

Lachkar, Zouhair

doi:10.1002/2013gl058726

Cited by 43 publications

(27 citation statements)

References 30 publications

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“…This is particularly relevant since observations have revealed a long-term trend toward stronger equatorward wind, strengthening the upwelling (Sydeman et al, 2014). We expect that a trend toward stronger upwelling would tend to exacerbate the progression toward undersaturation, as was found for the California Current System in an idealized wind enhancement experiment (Lachkar, 2014). Also a possible trend toward the upwelled waters becoming older and hence containing a larger amount of remineralized organic matter leading to lower pH and saturation states (Rykaczewski & Dunne, 2010) would tend to accelerate ocean acidification in the HumCS.…”

Section: Caveatsmentioning

confidence: 80%

Contrasting Impact of Future CO₂ Emission Scenarios on the Extent of CaCO₃ Mineral Undersaturation in the Humboldt Current System

et al. 2018

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The eastern boundary upwelling systems are among those regions that are most vulnerable to an ocean acidification‐induced transition toward undersaturated conditions with respect to mineral CaCO3, but no assessment exists yet for the Humboldt Current System. Here we use a high‐resolution (∼7.5 km) regional ocean model to investigate past and future changes in ocean pH and CaCO3 saturation state in this system. We find that within the next few decades, the nearshore waters off Peru are projected to become corrosive year round with regard to aragonite, the more soluble form of CaCO3. The volume of aragonite undersaturated water off Peru will continue to increase in the future irrespective of the amount of CO2 emitted to the atmosphere. In contrast, the development of the saturation state with regard to calcite, a less soluble form of carbonate, depends strongly on the scenario followed. By 2050, calcite undersaturation appears in the nearshore waters off Peru occasionally, but by 2090 in a high‐emission scenario (RCP8.5), ∼60% of the water in the euphotic zone will become permanently calcite undersaturated. Most of this calcite undersaturation off Peru can likely be avoided if a low emission scenario (RCP2.6) consistent with the Paris Agreement is followed. The progression of ocean acidification off Chile follows a similar pattern, except that the saturation states are overall higher. But also here, calcite undersaturated waters will become common in the subsurface waters under the RCP8.5 scenario by the end of this century, while this can be avoided under the RCP2.6 scenario.

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Section: Caveatsmentioning

confidence: 80%

Contrasting Impact of Future CO₂ Emission Scenarios on the Extent of CaCO₃ Mineral Undersaturation in the Humboldt Current System

et al. 2018

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“…One promising approach to understanding the processes underlying the CU variability (e.g., flow path and changes in p) is utilizing an eddyresolving numerical model for the CCS [Gruber et al, 2011[Gruber et al, , 2012Hauri et al, 2013aHauri et al, , 2013bLachkar, 2014]. Such higher-resolution models must be capable of resolving fine-scale CU dynamics on the order of 5-10 km observed in this study.…”

Section: Implications For Shelf O 2 and Phmentioning

confidence: 99%

Seasonal advection of Pacific Equatorial Water alters oxygen and pH in the Southern California Bight

et al. 2015

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Chemical properties of the California Undercurrent (CU) have been changing over the past several decades, yet the mechanisms responsible for the trend are still not fully understood. We present a survey of temperature, salinity, O2, pH, and currents at intermediate depths (defined here as 50–500 m) in the summer (30 June to 10 July) and winter (8–15 December) of 2012 in the southern region of the Southern California Bight. Observations of temperature, salinity, and currents reveal that local bathymetry and small gyres play an important role in the flow path of the California Undercurrent (CU). Using spiciness (π) as a tracer, we observe a 10% increase of Pacific Equatorial Water (PEW) in the core of the CU during the summer versus the winter. This is associated with an increase in π of 0.2, and a decrease in O2 and pH of 30 μmol kg−1 and 0.022, respectively; the change in pH is driven by increased CO2, while total alkalinity remains unchanged. The high‐π, low‐O2, and low‐pH waters during the summer are not distributed uniformly in the study region. Moreover, mooring observations at the edge of the continental shelf reveal intermittent intrusions of PEW onto the shelf with concomitant decreases in O2 and pH. We estimate that increased advection of PEW in the CU could account for approximately 50% of the observed decrease in O2, and between 49 and 73% of the decrease in pH, over the past three decades.

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“…Eastern boundary upwelling systems (EBUS) may be particularly prone to such modifications of atmospheric CO 2 -driven ocean acidification, because of the key role of the coastal upwelling process, which makes these systems naturally low in pH and Ω. Thus, relatively small changes in the intensity of upwelling in these systems may cause substantial changes in the rate of progression of ocean acidification (e.g., Feely et al 2008, Hauri et al 2009, Gruber 2011, Hofmann et al 2011, Alin et al 2012, Harris et al 2013, Rhein et al 2013, Bates et al 2014, Lachkar 2014, Williams et al 2015.…”

Section: Introductionmentioning

confidence: 99%

Climatic modulation of recent trends in ocean acidification in the California Current System

Turi

Lachkar

Gruber

et al. 2016

Environ. Res. Lett.

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We reconstruct the evolution of ocean acidification in the California Current System (CalCS) from 1979 through 2012 using hindcast simulations with an eddy-resolving ocean biogeochemical model forced with observation-based variations of wind and fluxes of heat and freshwater. We find that domain-wide pH and arag W in the top 60 m of the water column decreased significantly over these three decades by about −0.02 decade −1 and −0.12 decade −1 , respectively. In the nearshore areas of northern California and Oregon, ocean acidification is reconstructed to have progressed much more rapidly, with rates up to 30% higher than the domain-wide trends. Furthermore, ocean acidification penetrated substantially into the thermocline, causing a significant domain-wide shoaling of the aragonite saturation depth of on average −33 m decade −1 and up to −50 m decade −1 in the nearshore area of northern California. This resulted in a coast-wide increase in nearly undersaturated waters and the appearance of waters with 1 arag W < , leading to a substantial reduction of habitat suitability.Averaged over the whole domain, the main driver of these trends is the oceanic uptake of anthropogenic CO 2 from the atmosphere. However, recent changes in the climatic forcing have substantially modulated these trends regionally. This is particularly evident in the nearshore regions, where the total trends in pH are up to 50% larger and trends in arag W and in the aragonite saturation depth are even twice to three times larger than the purely atmospheric CO 2 -driven trends. This modulation in the nearshore regions is a result of the recent marked increase in alongshore wind stress, which brought elevated levels of dissolved inorganic carbon to the surface via upwelling. Our results demonstrate that changes in the climatic forcing need to be taken into consideration in future projections of the progression of ocean acidification in coastal upwelling regions.

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Effects of upwelling increase on ocean acidification in the California and Canary Current systems

Cited by 43 publications

References 30 publications

Contrasting Impact of Future CO₂ Emission Scenarios on the Extent of CaCO₃ Mineral Undersaturation in the Humboldt Current System

Contrasting Impact of Future CO₂ Emission Scenarios on the Extent of CaCO₃ Mineral Undersaturation in the Humboldt Current System

Seasonal advection of Pacific Equatorial Water alters oxygen and pH in the Southern California Bight

Climatic modulation of recent trends in ocean acidification in the California Current System

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Effects of upwelling increase on ocean acidification in the California and Canary Current systems

Cited by 43 publications

References 30 publications

Contrasting Impact of Future CO2 Emission Scenarios on the Extent of CaCO3 Mineral Undersaturation in the Humboldt Current System

Contrasting Impact of Future CO2 Emission Scenarios on the Extent of CaCO3 Mineral Undersaturation in the Humboldt Current System

Seasonal advection of Pacific Equatorial Water alters oxygen and pH in the Southern California Bight

Climatic modulation of recent trends in ocean acidification in the California Current System

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Contrasting Impact of Future CO₂ Emission Scenarios on the Extent of CaCO₃ Mineral Undersaturation in the Humboldt Current System

Contrasting Impact of Future CO₂ Emission Scenarios on the Extent of CaCO₃ Mineral Undersaturation in the Humboldt Current System