Dong-Ha Min’s Research:
Main goals of my research are (i) to better understand physical and biogeochemical processes in the marine environments, and (ii) to better delineate the responses of the environment to climate forcing, in various temporal and spatial scales. To achieve these goals I utilize physical and chemical analysis methods, analyze large-scale ocean data, and develop conceptual models. I conduct my research with 3 different spatial scopes: (i) global- to basin-, (ii) regional-, and (iii) local-scales. I measure trace gases such as sulfur hexafluoride (SF6) and chlorofluorocarbons (CFCs) in the ocean at ultra-trace level as decadal-scale transient tracers of ocean circulation and ventilation processes. This is to understand basin (i.e. Pacific Ocean) to regional (e.g. Gulf of Mexico) scale processes, and analyze basin-scale ocean data to detect decadal-scale ocean property changes in response to recent climate change. I also conduct coastal ocean observation in South Texas area to better understand various coastal processes.
I conduct my research in the following areas:
1. Large-scale ocean circulation and climate variability studies
2. Decadal- and basin-scale ocean data analysis for detecting climate impacts
3. Large-scale changes in marine biogeochemistry
4. Regional-scale ocean ventilation and climate variability studies
5. Coastal ocean observation
6. Climate-related gas exchange processes at the South Texas salt marsh / wetlands
7. Anomalous distribution of certain halogenated gas compounds in the ocean
8. Research for education technology
I. Large-scale ocean circulation and ventilation studies and ocean’s response to climate change
A. Basin-scale ocean circulation and ventilation study using anthropogenic CFC tracers in the world oceans
Transient tracer (e.g. CFC) information is crucial in understanding deep water formation rates, ventilation pathways and mixing, invasion rate of anthropogenic carbon to interior of the ocean. To better understand large-scale ocean ventilation processes and ocean’s response to the recent climate change, number of U.S. collaborators and I plan to observe CFCs and SF6 from a number of transect lines in the world oceans through the NSF-sponsored CLIVAR/CO2 repeat hydrography program in 6 major oceans between 2009 and 2014.
B. Decadal-scale change in ocean circulation and ventilation in the marginal seas: East Sea (Sea of Japan) and Gulf of Mexico
Although smaller in size, the ocean-like features in the Japan/East Sea in the Pacific provide useful insights and understanding of the open ocean processes and of prediction of future response of the oceans to recent climate change. Basin-wide CFC tracer measurements in 1999 showed decadal-scale ventilation feature of the sea with penetration of the anthropogenic tracers throughout the water column. Careful analysis of dissolved carbon species and CFCs measured in the East Sea indicates that the sea contains 0.50-0.06 peta grams (109 tons) of anthropogenic carbon, and it has penetrated all the way to the bottom over 3700 m throughout the water column. This is much higher inventory of the anthropogenic carbon than in the North Pacific, and similar to that of the North Atlantic Ocean (Park et al., 2006). Large-scale ventilation study is fairly scarce in the Gulf of Mexico in spite of its important roles for atmospheric water vapor transport, severe weather events, and being a precursor of the Gulf Stream. Deep measurements of tracers are even fewer. CFC tracers were measured in the upper 2000 m water column in the northwestern Gulf of Mexico during Omega-06 expedition (R/V Longhorn) in 2006. This study shows that CFC-11 has penetrated through the thermocline below 1000 meters indicating a decadal-scale ventilation time scale.
C. Decadal-scale variability of dissolved oxygen in the Southern Ocean, and the North Pacific and the North Atlantic Oceans during the past several decades
A careful analysis of historic ocean oxygen observations (e.g. World Ocean Database 2001) and temporally unvarying climatological oxygen data (e.g. World Ocean Atlas 2001), shows that the model predicted decadal-scale oxygen changes in the world oceans would be detectable from actual observations, and its magnitude would likely exceed the typical error of estimated oxygen trends by previous studies. Detailed statistical analysis of dissolved oxygen in the Southern Ocean during the last several decades shows the potential and challenges of detecting large-scale oxygen changes in the ocean as a proxy of ocean circulation change in response to recent global warming.
II. Coastal Ocean Observation
A. Continuous monitoring of environmental parameters at UTMSI Pier in the Aransas Pass tidal inlet, TX
I investigate the coastal water and material exchange processes observed at the MSI research pier in collaboration with Tony Amos (MSI). The Aransas Pass tidal inlet is strategically important location to observe major water exchanges between the offshore and bay waters of South Texas, to investigate transports of plankton and fish larvae, and to estimate exchange of terrestrial/estuarine biogeochemical materials. I have installed a vertical profiling sonde system at the pier to continuously monitor the whole water column (10-12m) at the interface between the Gulf of Mexico and the local estuaries/bays. The high frequency multi-parameter data are valuable not only in understanding the ordinary tidal exchange processes, but also in capturing short-term weather events of which data are often missed in conventional observations. I am also closely collaborating with Mission-Aransas NERR research team (Dr.Buskey) in observation strategies and operation.
B. Repeated nearshore hydrographic surveys off Port Aransas, TX
Land-Sea connection through tidal inlet and biogeochemical processes, particularly during episodic events, are not very well understood. I have been conducting a offshore repeat hydrography survey off Port Aransas in collaboration with C. Shank (MSI) to obtain baseline information. We seek a possibility of extending the NERR and MSI pier observation network to the offshore area to better delineate connection between terrestrial environment and coastal ocean.
C. Dissolved CFC observations at local bays and tidal inlet in South Texas
III. Climate-related trace gases in the atmosphere
A. Gas exchange processes of methyl halides at local wetlands and salt marsh habitats
I have collaborated with Dr.Rhew (UC Berkeley) to investigate land-air gas exchange processes some climate-related trace gases at the South Texas coastal wetlands. The pilot field campaigns with a number of flux chamber measurements was carried out in 2006 and 2008 at several vegetation habitats on local wetlands in Port Aransas. The result from Batis maritima (aka saltwort) showed the largest methyl bromide and methyl chloride fluxes to the atmosphere ever reported from salt marsh. Both gases are very important in interacting with the ozone layer in the stratosphere and their global budgets are yet to be refined. Stable isotope injection technique used to discriminate the plant’s uptake vs. export of the gases revealed that the measured gas flux is mostly net export from the plant (B. maritima).