Perspectives from the OPC-SAT blog series is dedicated to giving a voice to Ocean Protection Council Science Advisory Team (OPC-SAT) members to share their reflections on bridging the science policy boundary. The OPC-SAT is composed of 25 interdiscplinary scientists.
The difference in atmospheric pressure between the North Pacific high-pressure system and the US Southwest low pressure system manifests as strong wind blowing southward along the West Coast of North America. These winds, together with the Earth’s rotation (that is, the Coriolis force), drive water on the surface ocean away from the coast, and are replaced by deep, nutrient-rich waters that rise up to the surface.
This wind-driven oceanographic process, known as upwelling, nourishes the base of the food chain. It stimulates phytoplankton growth, which in turn supports large and diverse marine populations along the California coast and around the world — from tiny sardines to massive blue whales. However, human-induced global climate change (e.g., increasing atmospheric temperatures) will alter wind intensity and other important processes, leading to potentially profound alterations of California’s marine life and coastal fisheries.
Climate Change Likely to Increase Upwelling Events
Ecologists and fisheries biologists have long identified that understanding how climate change will impact upwelling is key to predicting potential changes to marine ecosystems. Indeed, for over 20 years, climate scientists and oceanographers have discussed this exact point. Accordingly, a new study published in Science last month makes significant strides in putting this longstanding scientific debate to rest.
By comparing 22 time-series studies on wind intensity from similar upwelling regions around the world (dating back to the 1940s), we tested a hypothesis proposed by oceanographer Andrew Bakun back in 1990. Bakun postulated that increasing greenhouse gas concentrations would lead to an intensification of upwelling-favorable winds. He proposed that warming could lead to larger temperature and pressure gradients between the oceans and land, produce stronger winds during summer, and drive more coastal upwelling.
The results of our study generally support Bakun’s hypothesis, suggesting that winds along the California Current have been increasing over the past 60 years, with rates of increase greater at more northerly latitudes.
Implications for California’s Ocean Health
Isn’t more upwelling good, in that it has the potential to benefit coastal areas by bringing more nutrients to surface waters? Yes, it is true that upwelling infuses surface waters with nutrients, but too much upwelling could, in fact, harm the ecosystem. For example, upwelling has major effects on ocean chemistry. Increasing upwelling may worsen ocean acidification and “de-oxygenation” of coastal waters. Persistently strong upwelling may also harm organism interactions by excessive transport of plankton (plants and animals that “go with the flow”) offshore and away from favorable coastal habitats. For upwelling, “moderate” is usually best for marine productivity.
What does this mean?
The complex and resilient nature of marine ecosystems makes it extremely difficult to predict the ecological effects of wind intensification in California and elsewhere where upwelling is prevalent. However, gaining insight into how major ocean processes like upwelling are and will be impacted by climate change is an important step in furthering our understanding of California’s ocean health, a priority issue for the state. California has put in place
a network of Marine Protected Areas to protect the ecosystem, and fish and wildlife managers are exploring ways to advance “climate-ready” fisheries. California is also significantly invested in the West Coast Ocean Acidification and Hypoxia Science Panel, an interdisciplinary collaboration across the region working to advance our understanding of the impacts of changing ocean chemistry on our marine environment.
The State of California is committed to taking a broad, holistic, ecosystem-wide approach to protecting its marine resources, and part of that effort includes managing for multiple stressors of ocean health. How, for example will upwelling intensification interact with coastal development and/or fisheries to alter ecosystem structure? Research such as that described herein serves this purpose by painting a clearer picture of how major ocean processes are changing with global warming. Working together, scientists, managers, and policy makers are beginning to put the pieces together of what the future oceans will look like, and how to help prepare for impending threats to the health of our marine ecosystems.
William J. Sydeman, Ph.D. is the President and Senior Scientist at the Farallon Institute
Hayley Carter, M.S. is a Project Scientist for the California Ocean Science Trust
Publication: “Climate change and Wind Intensification in Coastal Upwelling Ecosystems” Journal Article (Sydeman et al. 2014): https://www.sciencemag.org/content/345/6192/77