After completing our stations at the mouth of Amundsen Gulf, we transited to our next sampling area in the waters off of the Mackenzie River. We are sampling here to determine the role of freshwater from the river on the acidity of the ocean. The Mackenzie River is the largest river emptying into the Beaufort Sea; the only other being the Colville River which is one-tenth the size of the Mackenzie. Therefore the freshwater input from the Mackenzie may play an important role in the ocean chemistry of the Beaufort Sea and Arctic Ocean. The low alkalinity water from the river and high pCO2 (partial pressure) leads to decreased buffering capacity and higher acidity in the coastal waters.
While sampling near the river mouth, the water was clearly filled with silt from the river and the freshwater signal was high indicating that the river is playing an important role in the ocean chemistry of the area.
The purpose of this cruise is to learn about the ocean chemistry of the Arctic Ocean and in particular ocean acidification. So the question is, what is ocean acidification (OA) and why do we care? The short answer is that OA is the decrease in pH of the ocean due to increased free hydrogen ions in the water making it more acidic. We care because with this increasing acidity, the amount of carbonate minerals, in particular calcite and aragonite, available for animals to use for shell production and other metabolic needs, decreases and the ocean becomes under-saturated with respect to these carbonate ions.
Here is a diagram of the chemical reaction that leads to ocean acidification with the introduction of carbon dioxide, CO2, into the ocean. In the past century, since the Industrial Revolution, more and more CO2 is introduced from anthropogenic sources. The carbon dioxide enters the ocean, a sink for the CO2, where it combines with water and becomes carbonic acid which is very unstable. The carbonic acid breaks apart leaving a free hydrogen atom and bicarbonate. The resulting bicarbonate breaks up farther becoming a carbonate ion and another free hydrogen ion. Acidity is dependent on the number of hydrogen atoms in the water column so with more hydrogen atoms, you get a lower pH or higher acidity. On this cruise, dissolved inorganic carbon (DIC) and alkalinity are measured in order to derive pH. Alkalinity is the measure of the buffering capacity of water or the capacity of the water to neutralize acids. This buffering capacity is largely in the form of bicarbonate.
This graph shows the increase in CO2 concentration in the atmosphere since the 1950s and is the longest time series of data for this measurement. The ocean is a sink for much of this CO2 and has taken up between 1/3 and ½ of all anthropogenic CO2 emissions. Because the amount of CO2 in the ocean’s surface waters has increased considerably, the acidity of the ocean has increased due to the reaction outlined above. This increased acidity is highlighted in the Arctic regions where the ocean is naturally low in carbonate ion concentration due to ocean mixing patterns and increased solubility of CO2 in cold water.
The water samples collected on this cruise will help to build a better, more accurate, picture of how the increasing CO2 in our atmosphere will impact these fragile ecosystems.
The key to getting research accomplished both in the field and in the lab is a good team. Dr. Jeremy Mathis has put together a stellar group of young scientists in his Ocean Acidification Research Center (OARC) at University of Alaska-Fairbanks. I am having the pleasure of working with and learning from two of his current students while on board, Jessica Cross, a PhD student, and Stacy Reisdorph, a Masters student. Jessica and I sat down for a little chemistry lesson last night before she went on watch and I learned all about her research and her path to studying ocean chemistry…
Jessica takes a water sample after a deep cast
The USCGC Healy has become like a second home to Jessica as she has spent, in the past two years, more than 200 days aboard sailing mostly in the Bering Sea in order to collect data for her PhD research. A few years ago, when Jessica was a freshman at Rhodes College in Tennessee, she would never have imagined herself studying chemistry, let alone oceanography, as her first passions were books and writing. Now entering her fourth year of her PhD, she can’t imagine doing anything else and shows giddy excitement for ocean chemistry and endless enthusiasm for her work. Spending all of those days at sea after her initial coursework gave her a thorough understanding of basic oceanographic concepts and she explains how there is no better way to learn than to be at sea with other scientists who are willing to share their knowledge and experience. In the short time I have been at sea with Jessica, it is clear that she knows how to get work done efficiently and enjoys collecting samples for not just her own research but for the lab as a whole.
Jessica’s work focuses on ocean acidification in the Bering Sea as part of the Bering Ecosystem Study project (BEST). (Note: GOE participated in a BEST cruise in April/May 2008 in the Bering Sea…see Bering Sea Ice Expedition for more details) Jessica has been collecting and analyzing water samples from the Bering Sea for Dissolved Organic Carbon (DIC) and Alkalinity in order to determine the pH (measurement of acidity) of the water. Armed with this knowledge, she then can figure out the carbonate saturation state that is vital to the shell-building animals of the ocean, and in the Bering Sea in particular, the King Crab. The Bering Sea is a particularly interesting system, as is the Arctic Ocean, because of the variety of water mixing from river outflows, deepwater upwelling, surface water and ice melt creating an acidic environment in its natural state of equilibrium due to these various natural inflows of carbon dioxide. The question for the present and the future, is whether the increased anthropogenic carbon dioxide, and in turn the decreased pH in the Bering Sea, will affect the animals’ ability to adapt to their changing environment? Jessica seeks to quantify these changes and her excitement for the work is contagious.
In response to the imminent threat of climate change on the ocean, this expedition, the first National Science Foundation funded of its kind, will head to the Western Arctic Ocean to study ocean acidification. Human activities such as the burning of fossil fuels and changes in land use practices have led to an increase in atmospheric carbon dioxide and uptake of carbon by the ocean. These increased carbon dioxide concentrations lead to a decrease in the average pH of the surface waters of the ocean, a process called ocean acidification. The purpose of this expedition is to directly address questions of how human-induced climate change is affecting ocean chemistry in the Western Arctic Ocean.
The cold waters of the high latitudes are particularly vulnerable to ocean acidification due to increased solubility of carbon dioxide at low temperatures and low carbonate ion concentrations due to mixing patterns. This increased uptake in carbon dioxide along with the loss of sea ice and high rates of primary productivity over the continental shelves lead to increased ocean acidification in the Arctic Ocean and marginal seas. The rapid rates of change facing the high latitudes may have profound impacts on many organisms, particularly calcifying organisms that form calcium carbonate shells and hence need calcium carbonate minerals such as aragonite and calcite. Because of the sensitivity of these high latitude ecosystems to ocean acidification and their accelerated rates of change compared to lower latitudes, they become a real-time laboratory for understanding the changes and impacts of climate change on organisms and their possible cascading effects on the foodweb.
This study will be the first comprehensive assessment of the impacts of physical and biogeochemical processes on carbonate mineral saturation states and ocean acidification in the western Arctic Ocean and provide fundamental data for the understanding of ocean carbon cycle dynamics in the Pacific sector of the Arctic Ocean.
I am sitting in Anchorage as I write this post having just arrived here this afternoon. I am on my way to join Dr. Jeremy Mathis of the University of Alaska-Fairbanks and a team of scientists aboard the US Coast Guard Cutter Healy on an expedition studying the effects of climate change on ocean chemistry, particularly ocean acidification. I am flying out to Dutch Harbor tomorrow where we will board the ship and head North through the Bering Strait and into the Chukchi and Beaufort Seas. It should be a great expedition!
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