Researchers from several universities and NOAA offices, led by Liqing Jiang, have put together a set of interactive climatologies (long-term average conditions) and atlases depicting ocean acidification status across North American marine ecosystems. The maps show a variety of ocean acidification parameters including pH, pCO2, and aragonite and calcite saturation states that visualize ocean chemistry conditions and regional differences across US fisheries regions. The maps use a 1 ° x 1 ° resolution and are based on two decades of coastal observations of acidification conditions in North America’s large marine ecosystems (LMEs), many of them conducted by NOAA Ocean Acidification Program-funded scientists.
Simone Alin, a chemical oceanographer at NOAA’s Pacific Marine Environmental Laboratory, was one of the collaborators on this project, and we caught up with her to ask some questions.
Q: Simone, one of the first things we notice when looking at the maps is that Alaska is often a different color than other regions of the US? Why is that?
A: Areas like Alaska and the US West Coast (where I live) have colder water, and carbon dioxide (CO2) is more soluble in colder water. This results in an accumulation of CO2 in colder regions like Alaska. The higher CO2 levels lead to lower pH levels (which indicates higher acidity) and lower aragonite and calcite saturation states (which indicates lower favorability to shell building creatures). Waters in the North Pacific and Arctic coastal ecosystems are also naturally rich in CO2 because they are located in an area of the global ocean “conveyor belt” where some of the oldest, most CO2-rich ocean water surfaces after decades circulating below the surface. We say the water is “old” because it has been below the surface and out of contact with the atmosphere for a long time, allowing CO2 from decomposing phytoplankton and other living things to accumulate. Rivers can also bring high CO2 surface waters into coastal ecosystems. Together these natural processes create high background CO2 levels in the coastal waters of Alaska, which ocean acidification — the uptake of human-caused CO2 from the atmosphere — amplifies.
Q: The maps show some noticeable differences in characteristics at different depths. New hotspots appear or expand in deeper water. Could you tell us what’s going on here?
A: I’d love to! Unlike most people, I spend a lot of time thinking about invisible processes that happen on the bottom of the ocean.. With regard to chemistry and depth, a lot can be explained by phytoplankton. In the ocean, phytoplankton consume CO2 in sunlit surface waters through photosynthesis, and when they die and sink, the organic matter gets decomposed. This means it’s turned back into CO2, nutrients, and other breakdown products — much like what happens in a backyard compost pile. This decomposition process adds CO2 to local waters, so bottom habitats underneath productive surface areas (such as along the edge of sea ice) may end up as hotspots. Areas where circulation is more limited can also experience CO2 accumulation due to longer retention times of the water. Again, higher CO2 levels will cause acidity to increase and pH and saturation states to decrease. And these types of conditions can pose challenges to species.
NOAA oceanographer Simone Alin collects water samples aboard a research vessel.
Q: What might we miss when we look at this big picture level of resolution?
A: Great question. In addition to being spatially averaged over these 1° x 1° areas, they are also effectively averaged over the time period when these observations were made. This spatial and temporal averaging results in maps like these that can tell you something about what the regional average conditions have been over the past two decades, but these maps do not resolve smaller scale hotspots, extreme events, or long-term trends. Also, smaller area ecosystems like glacial inlets, which may be circulation-related hotspots, will not be reflected by these maps because observations from estuaries and glacial inlets were not included in the first version of this data product. We also don’t see the seasonal highs and lows of pCO2, pH, or saturation states. And finally, because we generally don’t get to sample these environments during the winter, these averages will be more representative of non-winter conditions.
Q: For the interested Alaskan who isn’t a researcher and wants to check out this tool, which OA indicator might be of most interest?
A: That really depends on what marine species or resources you care about most — whether it’s using a particular species for food, either for humans or your favorite ocean animal, or using their shells for cultural uses. If bivalves are important to you, you might want to look at the aragonite saturation maps for the depth closest to where your preferred species lives or its predator forages. For instance, nearshore harvesters might find the surface (0 m depth) maps the most relevant, whereas if you are interested in marine mammal food supply, you might choose to look at a depth that is closer to the depths of water they forage in. Similarly, if I was a crab fisher, I might look at the calcite saturation maps for the depth where my catch comes from. Some fish, including Pacific salmon species, may be sensitive to pH or CO2 levels (shown as fCO2 on the maps, which is very close to pCO2). Again, when thinking about how any of these species will be affected by OA, it’s important to keep in mind that the conditions in the maps represent average conditions, not the full seasonal range of conditions or extreme events. Also, we still have limited information about the critical sensitivity thresholds and duration of exposure for many species that will determine when they may experience harm from acidification.
Q: What can the maps show us about the capacity of our marine waters to resist ocean acidification?
A: The “Revelle factor” maps are actually some of the most interesting to me. These maps reflect the buffering capacity — or resistance to acidification — of marine waters. Cooler colors in these maps indicate areas where seawater is well buffered and can be expected to acidify more slowly with the ongoing uptake of human-emitted CO2. Warmer colors reflect waters that are less well buffered and are thus likely to acidify more rapidly with further addition of CO2. To me, these are the maps that best show why concern about acidification in Alaskan waters is high. Across depths, the average Revelle factor values are highest in Alaskan waters, reflecting relatively low buffering capacities and a propensity for rapid acidification in Alaska’s marine ecosystems.
The Revelle Factor is the buffering capacity — or resistance to acidification — of marine waters. Cooler colors in these maps indicate areas where seawater is well buffered and can be expected to acidify more slowly with the uptake of human-caused CO2. Warmer colors reflect waters that are less well buffered and are thus likely to acidify more rapidly with the ongoing addition of CO2. Alaska emerges as a a clear hotspot with high susceptibility to ocean acidification.
Q: What are some examples of ways these maps might be helpful, and how are they being used now?
A: One of the best ways to use these maps is to understand which areas are likely to experience impacts from acidification sooner than others. These may be areas with lower average saturation states or pH values, or with higher Revelle factor values (warmer colors on the map). They correspond to areas where conditions are worst or change is likely to be the most rapid, respectively. While Alaska is often described as being on the frontlines of climate change, some marine ecosystems within Alaska are more on the frontlines than others and may reach harmful levels of acidification for specific species sooner than others. Those regions would likely benefit from extra monitoring, management planning, or adaptation efforts. This could include setting up additional monitoring to assess the full range of seasonal variability and extreme events in areas where conditions appear to be worse or changing more rapidly. Along the West Coast, collaborations with Tribal and state Dungeness crab fishery managers have used information similar to this — maps of ocean conditions from forecast models as well as some of the observations that went into this new data product — to inform crab fishery management research and try to develop approaches to prepare the fishery to face rapidly changing ocean conditions.
Q: What are some big take-homes for the Alaska region based on this data visualization project?
A: Sustained ocean observations and data products like these climatologies and atlases are critical for understanding the status and rates of change of ocean conditions across North America’s marine ecosystems. As scientists, we can get really focused on making the high-quality observations necessary to measure the relatively slow, long-term changes in average conditions that are accruing in coastal waters year after year. However, when we zoom out and combine all of our hard-earned data sets to make maps like these, it becomes clear really quickly that marine environments in Alaska are likely to experience more rapid change than other North American regions.
Given the economic and cultural importance of marine resources of Alaska waters, understanding seasonality, extreme events, and rates of long-term change are really relevant for the region’s communities as well as the nation’s fisheries. These atlases provide high-quality information about average conditions over the past two decades, which is extremely helpful for comparison with other existing and future observations and model results. The background information provided by the atlases about average ocean conditions and likely ecosystem exposure to acidification is also critical for framing future research and management priorities, effort, and innovation in the region.
More about Simone:
Simone Alin has recently expanded her studies to Alaska waters and is working with Alaska partners to plan the next generation of ocean acidification observing efforts across Alaska’s large marine ecosystems. From the time she started at NOAA in 2007, she has studied biogeochemical conditions and processes in US West Coast coastal and estuarine ecosystems and the North Pacific Ocean. She leads a team of scientists who carry out ship-based carbon observation projects, including dedicated ocean acidification regional surveys and underway observations from ships of opportunity. Her research focuses on synthesizing and analyzing oceanographic data to understand how quickly ocean conditions are changing and what processes are most important to influencing them. She finds partnerships with other observational scientists and modelers; with fisheries, water quality, and other environmental managers; and policy and communication practitioners to be particularly rewarding. She is excited to be expanding her engagement with the Alaska OA community and learning more about how climate and ocean change are affecting Alaska’s ocean species and ecosystems.