Gray's Reef National Marine Sanctuary
Gray's Reef National Marine Sanctuary
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Data Buoy Science

MONITORING

Ocean Acidification and CO2 Monitoring

Ocean acidification (OA) is a global event altering the ocean chemistry due to the uptake of anthropogenic carbon dioxide (CO2). Continued burning of fossil fuels and land use change has caused atmospheric CO2 to increase. OA is of concern because the increase in seawater CO2 levels decreases the ocean's pH, affecting marine organisms requiring calcium carbonate to build their shells or skeletons. Recent research has indicated that the oceans act as a net repository or "sink" for atmospheric CO2, but that this sink is not uniform worldwide. Many coastal regions oscillate between being a CO2 sink and source depending on the time of year. The effects of ocean acidification have yet to be fully understood in coastal regions where biogeochemical processes are often vastly different from regions dominated by upwelling. To help educate the public about OA and what it can do to the marine organisms, the University of Georgia developed two educational posters.

Ocean Acidification in General

Poster explains ocean acidification in general.
Illustration by Amanda Camp under the direction of Dr. Scott Noakes and Eugene Wright, The University of Georgia.
Click here for larger view.

Effects of ocean acidification on coral calcification

Poster explains effects of ocean acidification on coral calcification.
Illustration by Amanda Camp under the direction of Dr. Scott Noakes and Eugene Wright, The University of Georgia.
Click here for larger view.


Dr. Scott Noakes on GRNMS data buoy

Dr. Scott Noakes replacing pCO2 sensor system on the Gray's Reef Data Buoy
(Photo: Sarah Fangman, GRNMS).

The coastal areas surrounding our continent (continental margins) are known to play a considerable role in determining global carbon cycling; however, little has been done to determine input from the coastal margins towards the total carbon "budget". Insufficient data exists to adequately determine the natural fluctuation ("flux") of air-sea CO2 with any level of confidence. The ability to explain the control mechanisms driving the variability of coastal partial pressure of CO2 (pCO2 or the concentration of CO2 in seawater) and pH is limited. Understanding these control mechanisms and how they affect pCO2 and pH is essential to predicting future changes in CO2flux, pH and carbonate saturation in our oceans. The primary reason that scientists are not able to determine the control mechanisms for coastal ocean regions is the absence of long-term high-resolution data. The highly dynamic coastal margin, with its combined terrestrial and oceanic input makes understanding this region a necessity for determining what mechanisms control the fluctuation of carbon dioxide.

Gray's Reef National Marine Sanctuary (GRNMS), located in the South Atlantic Bight (SAB) along the southeastern United States is situated in a very unique and dynamic region. It sits along the divide between the inner and middle shelf with water depths in the 20 m range. The water at the sanctuary is primarily controlled by the middle shelf oceanic dynamics, but during heavy rain events, it can be affected by freshwater plumes coming from the numerous rivers along the Georgia and South Carolina coast. Temperature also plays a major role in the SAB pCO2 variability with seasonal changes being apparent. Recent research along the mid-outer shelf has suggested that the SAB is a CO2 net sink and the inner shelf acts as a net source releasing pCO2 to the atmosphere. However, many factors such as ocean mixing, freshwater input, and Gulf Stream intrusions offer considerable input to the water chemistry at GRNMS.

The NOAA Pacific Marine Environmental Lab (PMEL), The University of Georgia (UGA), and GRNMS have been involved in monitoring pCO2 offshore Georgia for many years. PMEL established a monitoring station at GRNMS and has successfully collected high-resolution data since 2006. The PMEL station currently collects pCO2 at the air-sea interface and in the atmosphere; surface seawater temperature; and salinity. Surface water samples have also been collected at the site and analyzed for dissolved inorganic carbon (DIC), total alkalinity, (TA), dissolved oxygen (DO), pH and salinity to gain a concept for the TA-salinity relationship. As a result of these research efforts, a distinct relationship between the pCO2 concentrations and water temperature has been observed. As the seawater temperature increases, so does the pCO2. This phenomenon has been replicated every year since data collection began in 2006. The average air pCO2 as measured at GRNMS is approximately 400 micro-atmospheres (µatm). The level is typically exceeded in the water column during the warm summer months forcing CO2 out of the water into the atmosphere. This data demonstrates the cyclical nature of the middle SAB cycling from serving as a place where CO2 is stored to becoming a provider of CO2 to the atmosphere. Overall, atmospheric pCO2 is increasing at GRNMS at a rate of 0.78% per year and seawater pCO2 is increasing at a rate of 2.7% per year. The atmospheric pCO2 annual increase compares closely with the long-term monitoring data at Mauna Loa Observatory in Hawaii. However, the seawater pCO2 annual increase is approximately 1% higher at GRNMS than what has been recorded at Mauna Loa.

Air-sea, seafloor & temperature interface

Sea surface and atmospheric pCO2 and temperature as measured at GRNMS from 2006-2013.
Click here for larger view.
(Image: Dr. Scott Noakes, UGA).

Seafloor observatory

Seafloor observatory housing the high resolution pCO2 sensor and water quality probes.
(Photo: Dr. Scott Noakes, UGA).

What makes Gray's Reef unique among other locations offshore Georgia is its vibrant live bottom environment. Unlike the hard corals commonly found in the Florida Keys, much of Gray's Reef is composed of sponges and soft corals. In an effort to understand the environmental pressures occurring at Gray's Reef, UGA is also working to establish a seafloor observatory at the reef. Upon completion, this observatory will house a high resolution pCO2 sensor, high resolution pH sensor and water quality probes measuring temperature, dissolved oxygen, salinity, chlorophyll and turbidity. Conventional wisdom has always considered the coastal water column to be well mixed and that measurements collected at the surface should reflect conditions at the seafloor. However, preliminary data has shown that this is not always the case at GRNMS. To date, UGA has documented several events where the pCO2 on the surface and seafloor have not been in agreement.

Air-sea, seafloor & temperature interface

Air-sea interface pCO2 (green), seafloor pCO2 (blue) and temperature (red) collected at Gray's Reef during 2013.
Click here for larger view.
(Image: Dr. Scott Noakes, UGA).

It will take some time to understand the full impact of ocean acidification. The sponges and soft corals are generally more tolerant of environmental change than hard corals, but it is not known how these organisms living at Gray's Reef will be affected by changes in water chemistry due to increased CO2. With the seafloor observatory in place, it will open the door for scientists to more effectively study the benthic community. It is anticipated that continued CO2 research at Gray's Reef will explain how the benthic community will adapt and hopefully thrive as the Atlantic Ocean changes due to anthropogenic pressures.

This research, outreach, and monitoring effort has been funded by the NOAA Ocean Acidification Program, the Southeast Coastal Ocean Observing Regional Association (SECOORA), and Gray's Reef National Marine Sanctuary.


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