Bering Sea
The GAKOA Mooring in the Gulf of Alaska. Photo by Natalie Monacci

What We Know

​​The Gulf of Alaska is particularly vulnerable to ocean acidification due to global human emissions combined with natural local influences. These natural influences include cold water, ocean circulation, photosynthesis and respiration from phytoplankton and freshwater input. There are regional variations in these natural influences that fluctuate seasonally, creating a mosaic of conditions in different locations throughout the Gulf of Alaska at different times of the year.

Research on ocean acidification is being conducted throughout the Gulf of Alaska through a variety of avenues, including moored sensors, shorebased stations, shipboard measurements, and community sampling. As we continue to collect baseline data, an interesting picture of local conditions in the Gulf of Alaska is starting to emerge: some areas of the Gulf may serve as refuges from ocean acidification, and other areas appear to be developing into ocean acidification hotspots. While we work toward gathering enough information to clearly define regional conditions within the Gulf of Alaska, researchers are developing computational models to help us understand the forces that have historically driven carbon chemistry throughout this ocean basin.

Seasonal fluctuations
Carbon dioxide (CO2) is the main driver of ocean acidification. Increases in human carbon emissions are continuing to create more acidified conditions in the Gulf of Alaska, similar to the rest of the world. However, seasonal conditions impact this ongoing crisis in unique ways.

Gulf of Alaska Regional Profile

The Gulf of Alaska is defined by the curve of the southern coast of Alaska, stretching from Kodiak Island and the Alaska Peninsula in the west down to the Alexander Archipelago and Glacier Bay in the east. These are the traditional waters of the Alutiiq/Sugpiaq, Tlingit, Haida, Tsmishian and Eyak indigenous peoples. Important subsistence fisheries in the area include all five species of salmon, halibut, herring, and various shellfish species. The Gulf of Alaska supports highly productive commercial fisheries for the same species as well as groundfish such as rockfish, cod, pollock and flatfish.

Photo Gallery

↓Click to enlarge↓

Phytoplankton blooms play a major role in the seasonal cycle of CO2 in the Gulf of Alaska. In the summer, phytoplankton use up CO2 from the sunlit portion of the water for photosynthesis, which typically makes the water less acidic. These organisms eventually die and fall through the water column towards the bottom where they are metabolized by bacteria, creating a type of “carbon pump”. This results in more carbon-rich (and acidic) water at the bottom.

At the surface, CO2 levels are also generally higher in winter than summer months, and they are highest in southeast Alaska. This is primarily due to winter storms that vertically mix the water column, bringing corrosive water towards the surface. Weaker winds in the summer months allow deep water (> 300 ft) that is naturally high in CO2 to spread out over the continental shelf without mixing vertically.

Modeling Seasonal Dynamics of OA
Researchers have developed a computational model of the ocean circulation, chemistry, and biology for the Gulf of Alaska region to get a better idea of how the combination of these contributing processes may have already caused the system to change. They found that, while these processes push the chemical environment closer to harmful thresholds on a seasonal basis, there are natural fluctuations in the climate ocean system that temporarily accelerate ocean acidification every 6 to 10 years, causing “ocean acidification extreme events” in the offshore environment.

These natural fluctuations in chemical conditions are driven by the strength of the North Pacific Subpolar Gyre. This gyre is a large wind-driven system of circulating ocean currents affecting the Gulf of Alaska. When the gyre is strong, it brings more deep water rich in CO2 to the ocean’s surface. This can raise the acidity and corrosivity, creating extreme events that cause stress to sensitive organisms. However, when the gyre is weak, less carbon is delivered to the surface, which can dampen the observed ocean acidification effect or even reverse it. Because this fluctuation appears to occur on a cycle every decade or so, researchers are now focusing their efforts on the ways that this natural cycle is impacted by steadily increasing ocean acidification caused by human carbon emissions. If we can gain a better understanding of how these two phenomena interact, we may be able to predict when fluctuations will exacerbate regional OA in

What We Know About the Gulf of Alaska and OA

​​The Gulf of Alaska is particularly vulnerable to ocean acidification due to global human emissions combined with natural local influences. These natural influences include cold water, ocean circulation, photosynthesis and respiration from phytoplankton and freshwater input. There are regional variations in these natural influences that fluctuate seasonally, creating a mosaic of conditions in different locations throughout the Gulf of Alaska at different times of the year.

Research on ocean acidification is being conducted throughout the Gulf of Alaska through a variety of avenues, including moored sensors, shorebased stations, shipboard measurements, and community sampling. As we continue to collect baseline data, an interesting picture of local conditions in the Gulf of Alaska is starting to emerge: some areas of the Gulf may serve as refuges from ocean acidification, and other areas appear to be developing into ocean acidification hotspots. While we work toward gathering enough information to clearly define regional conditions within the Gulf of Alaska, researchers are developing computational models to help us understand the forces that have historically driven carbon chemistry throughout this ocean basin.

Seasonal fluctuations
Carbon dioxide (CO2) is the main driver of ocean acidification. Increases in human carbon emissions are continuing to create more acidified conditions in the Gulf of Alaska, similar to the rest of the world. However, seasonal conditions impact this ongoing crisis in unique ways.

Phytoplankton blooms play a major role in the seasonal cycle of CO2 in the Gulf of Alaska. In the summer, phytoplankton use up CO2 from the sunlit portion of the water for photosynthesis, which typically makes the water less acidic. These organisms eventually die and fall through the water column towards the bottom where they are metabolized by bacteria, creating a type of “carbon pump”. This results in more carbon-rich (and acidic) water at the bottom.

At the surface, CO2 levels are also generally higher in winter than summer months, and they are highest in southeast Alaska. This is primarily due to winter storms that vertically mix the water column, bringing corrosive water towards the surface. Weaker winds in the summer months allow deep water (> 300 ft) that is naturally high in CO2 to spread out over the continental shelf without mixing vertically.

Modeling Seasonal Dynamics of OA
Researchers have developed a computational model of the ocean circulation, chemistry, and biology for the Gulf of Alaska region to get a better idea of how the combination of these contributing processes may have already caused the system to change. They found that, while these processes push the chemical environment closer to harmful thresholds on a seasonal basis, there are natural fluctuations in the climate ocean system that temporarily accelerate ocean acidification every 6 to 10 years, causing “ocean acidification extreme events” in the offshore environment.

These natural fluctuations in chemical conditions are driven by the strength of the North Pacific Subpolar Gyre. This gyre is a large wind-driven system of circulating ocean currents affecting the Gulf of Alaska. When the gyre is strong, it brings more deep water rich in CO2 to the ocean’s surface. This can raise the acidity and corrosivity, creating extreme events that cause stress to sensitive organisms. However, when the gyre is weak, less carbon is delivered to the surface, which can dampen the observed ocean acidification effect or even reverse it. Because this fluctuation appears to occur on a cycle every decade or so, researchers are now focusing their efforts on the ways that this natural cycle is impacted by steadily increasing ocean acidification caused by human carbon emissions. If we can gain a better understanding of how these two phenomena interact, we may be able to predict when fluctuations will exacerbate regional OA in

Gulf of Alaska Regional Profile

The Gulf of Alaska is defined by the curve of the southern coast of Alaska, stretching from Kodiak Island and the Alaska Peninsula in the west down to the Alexander Archipelago and Glacier Bay in the east. These are the traditional waters of the Alutiiq/Sugpiaq, Tlingit, Haida, Tsmishian and Eyak indigenous peoples. Important subsistence fisheries in the area include all five species of salmon, halibut, herring, and various shellfish species. The Gulf of Alaska supports highly productive commercial fisheries for the same species as well as groundfish such as rockfish, pollock and flatfish.

Photo Gallery

↓Click to enlarge↓

Recent Studies

Modulation of OA by climate variability: Hauri et al. 2021

Modulation of OA by climate variability: Hauri et al. 2021

  • Gulf of Alaska ocean model simulation of chemical conditions for the years 1980-2013

Results

  • The apparent rate of ocean acidification in the Gulf of Alaska can be amplified, dampened, or even temporarily reversed by the strength of the North Pacific subpolar gyre.
  • When the gyre is strong, upwelling brings deep water that is rich in carbon dioxide to the surface ocean, creating more extreme ocean acidification conditions. When the gyre is weak, less carbon dioxide-rich water is delivered to the surface, dampening the ocean acidification conditions.
  • The strength of the gyre drives natural variability in chemical conditions. Strong phases of the subpolar gyre can cause extreme ocean acidification events, which may be harmful to sensitive organisms.

Regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry, and OA: Hauri et al 2020

Regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry, and OA: Hauri et al 2020

  • A new model for the Gulf of Alaska merges physical, biogeochemical, and freshwater hydrological models to reproduce ocean chemistry and ecosystem conditions from 1980-2013.

Results

  • Model output allows exploration of the biological and physical drivers of the inorganic carbon system, including parameters like aragonite saturation and pH which relate to ocean acidification.
  • Model output gives insight into spatial and temporal variability of inorganic carbon parameters in a large, dynamic, undersampled region.
  • An online tool allows easy visualization of the simulation, and includes over 100 ocean variables.
  • Near-bottom water on the Seward Oceanographic Line is continuously undersaturated between June and January due to upwelling and remineralization, which may be harmful to some organisms.
  • In coastal surface waters in summer and fall, freshwater input decreases the aragonite saturation state.

The importance of freshwater to spatial variability of Aragonite Saturation State in the Gulf of Alaska: Siedlecki et al 2017

The importance of freshwater to spatial variability of Aragonite Saturation State in the Gulf of Alaska: Siedlecki et al 2017

  • A high-resolution model for carbon dynamics in the GOA was developed to identify regions of high variability of Ω and test the sensitivity of those regions to changes in the chemistry of glacial meltwater discharge.

Results

  • The increase in aragonite saturation was nearly linear at 0.002 Ω per 100 µmol/kg increase in alkalinity in the freshwater runoff.
  • Local winds, biological processes, and freshwater forcing all contribute to the spatial distribution of Ω and identify which of these three is highly correlated to the variability in Ω.
  • Results indicate the importance of this climatically sensitive and relatively unconstrained regional freshwater forcing for Ω variability in the nearshore.

Implications

The combined effects of climate change and ocean acidification are altering the habitat of commercially important species in the Gulf of Alaska, exacerbating regional ocean acidification on seasonal time-scales. The use of computational models is quickly becoming an effective way to detect when biological and ecological thresholds have historically been crossed. This will facilitate future predictions of when the effects of ocean acidification may be particularly severe, allowing subsistence and commercial fisheries to adapt and respond.

Researchers

Jessica Cross

Claudine Hauri

Natalie Monacci

Natalie Monacci

Esther Kennedy

Brita Irving

Jessica Cross

Rémi Pagès

Chris Long

Addie Norgaard

Esther Kennedy

Gulf of Alaska Ecosystem Observatory

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