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Geographic variation of nearshore carbonate chemistry in the Gulf of Alaska


Amanda KelleyCollege of Fisheries and Ocean Sciences
University of Alaska Fairbanks



Distinctly different from the Holocene, we have entered the age of the Anthropocene- a
geologic epoch where human activities have been the primary driving force behind observable
shifts in climatic processes (Zalasiewicz et al. 2008; Waters et al. 2016). Ushering in a new
epoch has included notable global-scale changes to earth’s physical, chemical and biological
processes (Zalasiewicz et al. 2011). A byproduct of human activities, carbon dioxide- CO2, a
greenhouse gas, is largely responsible for these observed climatic shifts. CO2 released into the
atmosphere has directly modulated an increase in atmospheric temperature (IPCC 2013), and for
marine ecosystems in particular, these shifts have been manifested as an increase in seawater
temperature and a decrease in ocean pH, resulting from absorption of atmospheric CO2 by the world’s oceans, termed ocean acidification (hereafter OA). With the development of the first
ever pH sensor- seaFET (Martz, Connery, and Johnson 2010), studies of coastal pH have ably
demonstrated the complexity of natural nearshore dynamics, both spatially and temporally
(Kapsenberg et al. 2015; Kapsenberg and Hofmann 2016). This high pH variability confounds
our current understanding of the organismal sensitivity of OA as well as the reliable detection of
an anthropogenic signal in coastal ocean pH seascapes. Other abiotic factors influence the
frequency and amplitude of pH variability. Increasing freshwater discharge driven by climate
change accentuates and accelerates ocean acidification (Evans, Mathis, and Cross 2014). These
human-driven environmental changes are expected to not only continue, but intensify, as
atmospheric CO2 concentrations are predicted to increase over the next few centuries (IPCC
2013). As ocean pH continues to decrease and ocean temperatures continue to rise (IPCC 2013),
the combined impact of anthropogenic CO2 is already evident. The physical and chemical
changes highlighted above raise numerous questions about the long-term persistence and
sustainability of marine ecosystems. The phenomenon of OA across the planet has initiated the implementation of interconnected regional networks to monitor and report the chemical changes occurring within the carbonate system (Newton et al. 2014). The purpose of this global ocean acidification network (http://goa-on.org/) is to observe how acidification affects ecosystems from the tropics to the arctic within the context of marine resource viability. Thus far, three open ocean pH monitoring programs have identified a decline of 0.002 pH units per year (Bates and Peters 2007; Dore et al. 2009; González-Dávila et al. 2010). Specific to the United States, Alaskan aquaculture and fisheries marine resources are highly vulnerable to the effects of acidification due to high social and economic reliance on these marine resources (Ekstrom et al. 2015; Mathis et al. 2014). Scientists and researchers currently employ several methods to track acidification events and temporal trends in Alaskan coastal waters. Moored PCO2 sensors and ship-based bottle sampling of TCO2 and total alkalinity (TA) in deeper waters (Gulf of Alaska and Bering Sea); shore-based continuous PCO2 sampling by Burke-o-Lators (South east and central coasts); and Saildrones in South-central Prince William Sound (Dugan et al. 2017). While this effort has seen robust traction in the past few years, high spatial and temporal resolution measurements are still lagging in nearshore areas within the Gulf of Alaska (hereafter GoA).


The issue

Despite Alaska’s vast coastlines and vital fisheries, little is known about how ocean
acidification (OA), a decline in ocean pH due to the absorption of anthropogenic carbon dioxide
by the world's oceans, affects the nearshore environment. Nearshore ecosystems help to protect
the coastline and provide important habitat for marine animals. Because these ecosystems are
highly dynamic and complex, it has been challenging to accurately monitor changes in ocean
chemistry in coastal waters, especially in Alaska. With few baseline ocean pH records in place, it
is difficult to determine the human-caused and natural influences on ocean pH variability.
Measuring OA is increasingly important to aid our understanding of how marine ecosystems will
respond to global ocean change. Current advances in pH sensor technology have led to increased
OA monitoring along the west coast of the United States. As mounting evidence suggests marine
species vital to Alaska’s fisheries are threatened by OA, managing the threat of ocean
acidification on a local scale is becoming a concern for policymakers and managers in the state.

Why is this an Alaska Sea Grant project?

The key to determining the role carbon-induced forces play in restructuring nearshore biological communities lies in increased understanding of present-day
carbonate system dynamics. Increasing our knowledge of the biological and physical drivers that
regulate nearshore pH dynamics will help detangle natural vs. human-caused pH variability.
Also, it will bring Alaska to the forefront of OA monitoring along with other states that have
deployed similar pH sensor networks. For example, the National Science Foundation’s Santa
Barbara Coastal Long Term Ecological Research program has had a pH sensor network in place
since 2011 (http://sbc.lternet.edu//research/index.html). Similarly, the Northwest Environmental
Moorings program in the Puget Sound in Washington State collaborates with the Northwest
Association of Networked Ocean Observing Systems to operate a similar pH sensor network
(http://nwem.ocean.washington.edu/index.shtml). These coastal observing systems provide vital
and high-quality data to resource managers and resource users, yielding crucial information
necessary to develop and plan OA mitigation strategies.

How will researchers conduct their study?

I propose to establish pH sensor networks within two regions in the Gulf of Alaska- GOA--leveraging newly acquired instrumentation (from the NSF’s Alaska EPSCoR program- PI Kelley is a senior researcher and the Kachemak Bay National Estuarine Research Reserve, roughly $150,000 worth of equipment) to characterize baseline high-frequency pH dynamics in Kachemak Bay (Homer, AK) and Lynn Canal (Juneau, AK). These communities are vital coastal areas for commercial, recreational and substance activities. Furthermore, these regions ‘bookend’ the Gulf of Alaska, likely with differing physical oceanographic conditions--circulation, temperature, freshwater influx and primary productivity, providing a comparison of the how these forces differentially influence the nearshore carbonate chemistry of each region.