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Exploring the Relationship between Water Temperature and Dissolved Oxygen in the Gulf of Mexico Introduction: Every summer, the Gulf of Mexico experiences reduced concentrations of dissolved oxygen at the mouth of the Mississippi River. The phenomenon has created an “ocean dead zone” where biological communities suffer from falling growth rates and reduced fecundity [Dodds, 2006; Prasad et al., 2011]. The hypoxic conditions generally occur below the pycnocline from as early as February to October through June, July, and August [Rabalais et al., 2001]. Nitrogen and phosphorous nutrient loading from Mississippi River effluent has been proposed as the cause of the hypoxic ocean conditions, as spatial and temporal variability in the distribution of the hypoxia is correlated to the amplitude and phasing of the Mississippi River discharges and nutrient flux [Dodds, 2006; Rabalais et al., 2001]. Hypoxic conditions in the Gulf of Mexico can take a severe toll on biological communities, from the bottom of the food chain all the way up to the top. In some situations, hypoxic conditions can actually increase phytoplankton production, usually the case with eutrophication, but decrease the zooplankton population by causing decreases in egg production and hatching success [Elliot et al., 2012]. Zooplankton community structure is generally altered under hypoxic conditions, which can contribute to problems higher up the food chain [Elliot et al., 2012; Roman, 1993]. Fish, crabs, mollusks, and other aquatic organisms must have adequate levels of dissolved oxygen in the water column to respire and survive. Low levels of dissolved oxygen can lead to lethargic behavior in larger organisms, or avoidance of hypoxic areas by fish [NOAA, 2008]. Generally, higher trophic level fish require higher levels of dissolved oxygen to respire [Addy and Green, 1997]. Thus, the lucrative recreational and commercial red snapper fishing industries in the Gulf of Mexico must avoid fishing in the hypoxic regions during summer months, as the fish evade hypoxic regions. While hypoxic conditions have been linked to eutrophication in the Gulf of Mexico, there are also other factors at play. There is a direct relationship between temperature and dissolved oxygen since the solubility of oxygen decreases as the water temperature increases. Salinity and dissolved oxygen exhibit the same trend; an increase in salinity will decrease oxygen’s, or any gas’s, solubility in the water [NOAA, 2008]. The Chesapeake Bay experiences similar summer hypoxic conditions to the Gulf of Mexico, conditions that have been linked to changes in temperature, salinity, and dissolved nutrient concentrations in combination [Prasad et al., 2011]. Thus, the research question at hand is as follows: Is the summer hypoxia in the Gulf of Mexico caused primarily by nutrient loading or does ocean temperature play a role? This research question aims to address how dissolved oxygen levels may change with respect to climate change. As water temperatures continue to increase in the Gulf of Mexico, the water’s ability to absorb oxygen will decrease, potentially leading to increases in hypoxic ‘dead zones’ throughout the Gulf. This poses serious threats to maintaining biological community structure and raises a variety of implications for future fisheries management in the Gulf of Mexico. Hence, understanding how the Gulf’s water conditions may change is crucial to preparing for future resource management.

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Methods: Obtaining Data World Ocean Atlas 2009 one degree water temperature and dissolved oxygen monthly climatologies were collected from http://www.nodc.noaa.gov/OC5/WOA09/netcdf_data.html. The NOAA National Oceanographic Data Center (NODC) provides netCDF downloads of annual, seasonal, and or monthly climatologies for a variety of ocean parameters in one degree or five degree grid sizes. The World Ocean Atlas (WOA) is produced by the Ocean Climate Laboratory of the NODC. The first version of the WOA was created in 1994 and has been updated in 1998, 2001, 2005, 2009, and now 2013 using in situ data measurements. Measurements are objectively-analyzed to create global grids at one degree and five degree scales. WOA datasets contain measurements at 33 depth intervals and span across all twelve months, four seasons, or one year. Data used to prepare the WOA, and all updates, come from the World Ocean Database (WOD - http://www.nodc.noaa.gov/OC5/SELECT/dbsearch/dbsearch.html). The WOD includes in situ data collected from ocean station data; mechanical bathythermograph profiles; expendable bathythermograph profiles; conductivity, temperature, depth casts; undulating oceanographic recorder profiles; profiling floats (potentially Argo probes); moored buoys; drifting buoys; gliders; and autonomous Pinniped bathythermograph profiles. Data Processing and Analysis All data processing was carried out using MATLAB R2013b (MathWorks, Inc., Natick, Massachusetts, United States) in a script titled Livermore_Project_Script.m. To begin data preprocessing, both netCDF files obtained from the NODC website (temperature_monthly_1deg.nc and dissolved_oxygen_monthly_1deg.nc). Both datasets were broken down into a variety of variables including latitude, longitude, time, and depth. To create an annual climatology, both climatological datasets were averaged across all twelve months, creating annual temperature and dissolved oxygen variables. Then both datasets were indexed to select only sea surface data (the first depth measurement). These datasets were mapped for just the Gulf of Mexico. The following coordinates were used to select the Gulf of Mexico region within the ‘axesm’ command: 17 º – 35º N and 80º – 100 º W. Using the original climatologies, surface temperature and dissolved oxygen were indexed for winter months (December, January, and February) and summer months (June, July, and August). Then they were both averaged across to create winter and summer surface maps for both parameter. To create seasonal climatologies for smaller inshore and offshore regions of the Gulf of Mexico, the original climatologies were indexed to select these regions, and only surface data. Regions were selected after creating the three aforementioned maps, which allowed for selection of areas where changes were more drastic inshore and less drastic offshore. The outputs were then averaged across longitude and latitude and plotted as a function of time. Finally, to create winter and summer depth profiles within each subset region, the original climatologies were again indexed for the longitudes and latitudes of the smaller regions of the Gulf for both the

[NAME REMOVED]– EOS 321 summer and winter seasons. The new indexed variables were then averaged across longitude, latitude, and time. Seasonal outputs were subplotted as a function of depth. Results:

Figure 1. Maps of Gulf of Mexico annual sea surface dissolved oxygen concentration and temperature in situ climatologies averaged across all twelve months. Climatological data obtained from http://www.nodc.noaa.gov/OC5/WOA09/netcdf_data.html.

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Figure 2. Maps of Gulf of Mexico winter sea surface dissolved oxygen concentration and temperature in situ climatologies averaged across summer months (December, January, and February). Climatological data obtained from http://www.nodc.noaa.gov/OC5/WOA09/netcdf_data.html.

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Figure 3. Maps of Gulf of Mexico summer sea surface dissolved oxygen concentration and temperature in situ climatologies averaged across summer months (June, July, and August). Climatological data obtained from http://www.nodc.noaa.gov/OC5/WOA09/netcdf_data.html.

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Figure 4. Annual surface dissolved oxygen and sea surface temperatures averaged across latitude and longitude for inshore and offshore regions of the Gulf of Mexico. The inshore region ranges from 27.5-20.5 degrees N and 85.5-88.5 degrees W and the offshore region ranges from 23.526.5 degrees N and 87.5-90.5 degrees W. Climatological data obtained from http://www.nodc.noaa.gov/OC5/WOA09/netcdf_data.html.

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Figure 5. Depth profiles of dissolved oxygen and water temperature for winter (averaged over December, January and February) and summer (averaged over June, July, and August) in inshore and offshore regions of the Gulf of Mexico. The inshore region ranges from 27.5-20.5 degrees N and 85.5-88.5 degrees W and the offshore region ranges from 23.5-26.5 degrees N and 87.5-90.5 degrees W. Climatological data obtained from http://www.nodc.noaa.gov/OC5/WOA09/netcdf_data.html. Mapping DO and SST Annual surface dissolved oxygen concentrations were the highest inshore just south of Mississippi, Louisiana, and the Florida panhandle (Figure 1. top image). Dissolved oxygen concentrations approached 5.25 ml/l in this region, while the majority of the Gulf had concentrations ranging between 4.5 and 5 ml/l. Sea surface temperature was lower in the same geographic region as dissolved oxygen concentrations were higher (Figure 1. bottom image). Inshore regions in the Northern portion of the Gulf reached 24º C. The rest of the Gulf ranged between 25º and 27º C. In the winter, sea surface temperature was substantially lower in the same northern inshore region. Temperatures approached 18º C in the inshore region while most of the Gulf hovered around 24º - 25º C (Figure 2. bottom image). There is a parallel trend in surface dissolved oxygen levels in the northern inshore region, to the west of the Florida Gulf

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shoreline and south of the Florida panhandle (Figure 2. top image). Dissolved oxygen concentrations reach 5.5 ml/l in the northeastern inshore region of the Gulf, while the middle of the Gulf ranges from 4.5º – 5º ml/l. Finally, in summer months, there is similar spatial trend in sea surface temperature. For the entire Gulf, temperatures remain within 27.5º and 28º C (Figure 3. bottom image; color bar at different scale from Figures 1 and 2). As for summer dissolved oxygen levels at the surface, concentrations are still the highest at in the northeaster portion of the Gulf, where they approach 5 ml/l (Figure 3. top image). The rest of the Gulf is closer to 4.4 – 4.7 ml/l. Annual DO and SST Inshore and Offhsore Sea surface dissolved oxygen concentrations differed between inshore and offshore regions throughout the course of the year (Figure 4. top two images). Concentrations were generally higher in the inshore region than in the offshore region, except for the month of September, when both regions had concentrations of about 4.5. For both areas, the concentrations of dissolved oxygen were generally higher at the end of winter and into spring (February through May) and lower during summer months (June through September). Inshore and offshore regions exhibited a similar annual temperature pattern, though the inshore region’s pattern had a larger range of temperature values (Figure 4. bottom two images). The inshore region ranged from about 20º C in February to almost 30º C in August. The offshore region ranged from approximately 23º C in February to around 29.5º in August. For both inshore and offshore regions, there is an inverse relationship, or negative correlation, between dissolved oxygen concentration and temperature; as temperature increases, dissolved oxygen decreases. DO and SST as Functions of Depth As depth increased from 0-500m, the concentration of inshore dissolved oxygen during the winter decreased from just over 5 ml/l to around 2.7 ml/l (Figure 5. top left image). From 500-1500m, the concentration increased from 2.7 ml/l to just under 5 ml/l. The summer inshore dissolved oxygen concentration was very similar, except that for approximately the first hundred meters, the concentration was lower, since it started at 4.6 ml/l at the surface. There was a fair amount of variation throughout the depth profile. For the offshore region, there was a very similar pattern (Figure 5. bottom left image). The two regions’ profiles were almost identical at depth, but the first 100 meters differed since the offshore summer and winter profiles converged within the first 50 meters. Offshore surface dissolved oxygen in the winter started at 4.75 ml/l while summer profile starts at 4.5 ml/l at the surface. Temperature depth profiles for the inshore and offshore regions were almost identical for the summer seasons (Figure 5. right top and bottom images). In both regions, the summer profile starts around 29º C and decreases to 4º C as depth increases from 0 to 1500 meters. The winter profiles were quite similar as well, though the inshore region exhibits lower surface temperatures (top 50 meters or so) near 22º C, while the surface temperature offshore starts at 24º C and immediately starts to decrease with increasing depth. There is a clear relationship between dissolved oxygen concentration and water temperature at the surface, as well as at depths greater than 500 meters for both regions. Both offshore and inshore regions have cooler surface temperatures and higher dissolved oxygen concentrations in the winter. When water temperature is higher in the summer in both areas, the

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dissolved oxygen concentration is lower. For both seasons and both regions, as depth increases up to 500 meters, temperature decreases and dissolved oxygen concentration decreases until it reaches the oxygen minimum zone. From approximately 500 meters to 1500 meters of depth, temperature continues to decrease and dissolved oxygen increases. Discussion: It is clear that there is a strong relationship between dissolved oxygen concentration and water temperature. The seasonal trends illustrated in Figure 4 and the depth profiles in Figure 5 demonstrate an inverse relationship between dissolved oxygen concentration and water temperature. The relationship between dissolved oxygen and temperature from the surface to approximately 500 meters in depth, at which point the oxygen minimum zone occurs, is a direct relationship, but this is most likely attributed to biological factors that have not been included in the scope of this study. NOAA [2008] explains that as water temperature increases, the solubility of oxygen within it decreases. Figures 4 and 5 explore this phenomenon temporally and as a function of depth. Figures 2 and 3 indicate seasonal changes in sea surface temperature and surface dissolved oxygen concentrations that also provide support to the concept of decreasing oxygen solubility with increased temperature; in locations where or times when the temperature is higher, the dissolved oxygen is generally lower. All data collection and analysis support the idea of a strong relationship. It is crucial to note that upwelling occurs in the northern portion of the Gulf of Mexico, which brings cooler nutrient rich water from the bottom of the ocean up to the surface. Therefore, the dissolved oxygen levels in upwelling areas will be higher, as they are in the northern portion of the Gulf below the Florida panhandle. While studies [see Dodds, 2006; Rabalais et al., 2001; and Engle et al., 1997] indicate that there is a hypoxic dead zone near the mouth of the Mississippi River especially in estuaries, these dangerous hypoxic conditions did not show up using analysis of WOA 2009 annual climatologies. This may be attributed to the large 1 degree resolution of the dataset, since it is designed to be mapped globally. It could also be attributed to the fact that the nutrient loading and algal blooms which decrease dissolved oxygen concentrations occur sporadically and may be averaged out by only analyzing climatologies of data spanning over the last 60 years. As explained by Prasad et al. [2011], for the Chesapeake Bay, dissolved oxygen levels depend on water temperature, salinity, and nutrient concentrations in combination. Therefore, it is reasonable to assume that a similar relationship between the nutrients and ocean salinity and temperatures is taking place in the Gulf of Mexico, but further research must be carried out to gain a deeper understanding of this relationship in the northern Gulf of Mexico hypoxic zone. The analysis of seasonal changes in temperature and dissolved oxygen suggests that there is a very strong relationship between the two ocean quality parameters. Nonetheless, temperature is likely not the cause of the summer dead zone in the northern portion of the Gulf, since temperature changes affect the entire Gulf, though the seasonal temperature shift is smaller in offshore regions. In addition, the upwelling water in the northern region should help to offset the summer warming of the water and the decrease in dissolved oxygen. Even so, according to a variety of studies, the dead zone still occurs each summer. Therefore, eutrophication from agricultural runoff carried into the ocean by the Mississippi River is likely the cause of the

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hypoxia, as suggested by Dodds [2006], Rabalais et al. [2001], and Engle et al. [1997]. Thus, management measures should be focused on limiting agricultural runoff in order keep phytoplankton and zooplankton communities and trophic structures in balance. It is also important to consider that increasing ocean temperatures due to climate change may interact synergistically with nutrient loading to create larger and longer-lasting hypoxic zones. Future management of the Gulf of Mexico resources including fisheries must be adaptive and incorporate a variety of changing ocean parameters. While the global netCDF datasets from the WOA were adequate to investigate seasonal trends in water temperature and dissolved oxygen, there are other datasets available that may have been better for analyzing the Gulf of Mexico dead zone specifically. Since the study region was not selected at the initiation of this research project, the one degree resolution global datasets were a good option. Nonetheless, there are regional climatologies specifically for the Gulf of Mexico at 0.25 and 0.10 degree resolutions for all the same study parameters used during this project (see http://www.nodc.noaa.gov/OC5/regional_climate/GOMclimatology/). The higher resolutions may have helped to reveal the dead zone near the mouth of the Mississippi River, which our data was unable to point out. The hypoxic conditions in the Gulf are most intense at the oxygen minimum zone, caused by eutrophication, stratification, and respiration of biological organisms throughout the water column [Nunnally, 2013]. The oxygen minimum zone is clearly visible near 500 meters in the inshore and offshore region of the Gulf of Mexico, since the dissolved oxygen level decreases from the surface until approximately 500 meters of depth, at which point it increases with increasing depth (Figure 4). Nevertheless, the hypoxic zone was not observable at depth. Mapping of water temperature and dissolved oxygen concentration was carried out for 500 meters of depth, approximately the oxygen minimum zone, as determined by Figure 4 (refer to Appendix Items 1 and 2); the maps did not reveal the northern Gulf of Mexico hypoxic zone to the south of the Mississippi River and were therefore not included in the results. While the oxygen minimum zone was demonstrated clearly in Figure 4, the maps did not show any areas where the DO was even less than it was in surrounding areas. Another potential option for future work in isolating the hypoxic zone may include looking at individual years of in situ data for the Gulf of Mexico, rather than at climatologies averaged across 60 years. To further investigate the relationship between dissolved oxygen and temperature fluctuations, it would also be beneficial to obtain other seasonal climatologies from the World Ocean Atlas 2009 (see http://www.nodc.noaa.gov/OC5/WOA09/netcdf_data.html) for salinity and for nutrients, especially phosphorous and nitrogen as researched by Dodds [2006]. This would allow for comparisons between dissolved oxygen and nutrient loading, which may lead to algal blooms that cause dead zones due to decomposition of algal detritus. Looking at chlorophyll A concentrations using in situ or remote sensing datasets could also be interesting because these data would point out areas and times in which algal blooms are more common. Seasonal nutrient concentration measurements from the Mississippi River could also help to investigate the connection between agricultural runoff, dissolved oxygen, temperature, and salinity in the Gulf of Mexico.

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References: Addy, K., and L. Green (1997), Dissolved oxygen and temperature, FactSheetNo.96-3, 4 pp., University of Rhode Island College of Resource Development Department of Natural Resources Science Cooperative Extension. Dodds, W. K. (2006), Nutrients and the “Dead Zone”: the link between nutrient ratios and dissolved oxygen in the northern Gulf of Mexcio, Frontiers in Ecology and the Environment, 4(4), 211-217. Elliot, D. T., J. J. Pierson, and M. R. Roman (2012), Relationship between environmental conditions and zooplankton community structure during summer hypoxia in the northern Gulf of Mexico, Journal of Plankton Research, 34(7), 602-613. Engle, V. D., J. K. Summers, and J. M. Macauley (1999), Dissolved oxygen conditions in northern Gulf of Mexico estuaries, Environmental Monitoring and Assessment, 57, 1-20. NOAA Ocean Service Education (2008), Dissolved Oxygen, http://oceanservice.noaa.gov/education/kits/estuaries/media/supp_estuar10d_disolvedox.html. Nunnally, C. C., G. T. Rowe, D. C.O. Thornton, and A. Quigg (2013), Sedimentary oxygen consumption and nutrient regeneration in the northern Gulf of Mexico Hypoxic zone, Journal of Coastal Research, 63, 84-96. Prasad M. B. K., W. Long, X. Zhang, R. J. Wood, and R. Murtugudde (2011), Predicting dissolved oxygen in the Chesapeake Bay: applications and implications, Aquatic Science, 73, 437-451. Rabalais, N. N., R. E. Turner, and W. J. Wiseman Jr. (2001), Hypoxia in the Gulf of Mexico, Journal of Environmental Quality, 30(2), 320-329. Roman, M. R., A. L. Gauzens, W. K. Rhinehart, J. R. White (1993), Effects of Low Oxygen Waters on Chesapeake Bay Zooplankton, Limnology and Oceanography, 38(8), 1603-1614.

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Appendix: Item 1. Summer (July through August) dissolved oxygen concentration and water temperature at 500 meters of depth – at the minimum oxygen zone based on depth profiles of DO

[NAME REMOVED]– EOS 321 Item 2. Winter (December through February) dissolved oxygen concentration and water temperature at 500 meters of depth – at the minimum oxygen zone

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Item 3. MATLAB Script for Data Analysis and Figure Generation %% Final Project (EOS 321) % Julia Livermore % Analyzing differences between sea surface temperatures and dissolved % oxygen levels in the Gulf of Mexico %Livermore_Project_Script.m clear all; close all; %% Preparing Temperature Data %commands to open, process, and plot temperature and temperature measurements at %the ocean surface %i. Opening variables temp_struct = ncinfo('temperature_monthly_1deg.nc'); Var_struct_temp = temp_struct.Variables; Dim_struct_temp = temp_struct.Dimensions; %Creating a cell array where each cell lists either the variable name or %dimension name var_names = {Var_struct_temp.Name}; %cell array of variable names dim_names = {Dim_struct_temp.Name}; %cell array of dimension names %i. Opening data %Ready to use the ncread command to acutally get the data in the %structures. clear %clear file information temp_depth = ncread('temperature_monthly_1deg.nc','depth'); %get temperature depth data temp_lat = ncread('temperature_monthly_1deg.nc','lat'); %get latitudes temp_lon = ncread('temperature_monthly_1deg.nc','lon'); %get longitudes temp_time = ncread('temperature_monthly_1deg.nc','time'); %get time temp_clim = ncread('temperature_monthly_1deg.nc','t_an'); %get climatology %ii. time averaging and indexing for whole climatology temp_mean = nanmean(temp_clim, 4); % time-averaged temperature data for plotting % Create surface climatology (1 = top depth, which is surface) temp_mean_surf = (temp_mean(:,:,1)); % Create averaged surface temperature for Winter temp_wint = (temp_clim(:,:,1,[1,2,12])); temp_winter = nanmean(temp_wint,4);

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% Create averaged surface temperature for Summer temp_sum = (temp_clim(:,:,1,6:8)); temp_summer = nanmean(temp_sum,4); %iii. data processing temp_lat = double(temp_lat); %convert to double precision temp_lon = double(temp_lon); temp_mean_surf = temp_mean_surf'; %flip rows and columns for surface temperature data temp_winter = temp_winter'; temp_summer = temp_summer'; %% Preparing DO Data %commands to open, process, and plot DO and DO measurements at %the ocean surface %i. Opening variables DO_struct = ncinfo('dissolved_oxygen_monthly_1deg.nc'); Var_struct_DO = DO_struct.Variables; Dim_struct_DO = DO_struct.Dimensions; %Creating a cell array where each cell lists either the variable name or %dimension name var_names = {Var_struct_DO.Name}; %cell array of variable names dim_names = {Dim_struct_DO.Name}; %cell array of dimension names %i. Opening data %Ready to use the ncread command to acutally get the data in the %structures. DO_depth = ncread('dissolved_oxygen_monthly_1deg.nc','depth'); %get DO depth data DO_lat = ncread('dissolved_oxygen_monthly_1deg.nc','lat'); %get latitudes DO_lon = ncread('dissolved_oxygen_monthly_1deg.nc','lon'); %get longitudes DO_time = ncread('dissolved_oxygen_monthly_1deg.nc','time'); %get time DO_clim = ncread('dissolved_oxygen_monthly_1deg.nc','o_an'); %get climatology %ii. time averaging and indexing for whole climatology DO_mean = nanmean(DO_clim, 4); % time-averaged DO data for plotting % Create surface climatology (1 = top depth, which is surface) DO_mean_surf = (DO_mean(:,:,1)); % Create averaged surface DO for Winter DO_wint = (DO_clim(:,:,1,[1,2,12])); DO_winter = nanmean(DO_wint,4); % Create averaged surface DO for Summer DO_sum = (DO_clim(:,:,1,6:8));

[NAME REMOVED]– EOS 321 DO_summer = nanmean(DO_sum,4); %iii. data processing DO_lat = double(DO_lat); %convert to double precision DO_lon = double(DO_lon); DO_mean_surf = DO_mean_surf'; %flip rows and columns for surface temperature data DO_winter = DO_winter'; DO_summer = DO_summer'; %% Visualizing data - mean DO and mean SST %i. mapping mean annual DO and SST figure subplot(2,1,1) load coast axesm('MapProjection','mercator','MeridianLabel','on','ParallelLabel',... 'on','mlinelocation', 20,'plinelocation',5,'mlinelocation',5,... 'maplatlimit',[17 35],'maplonlimit',[-100 -80],'grid' ,'on'); framem hold on; hidem(gca); %Hides rectangle border around map set(gcf,'color','w') %Background color of the figure to white surfm(DO_lat,DO_lon,DO_mean_surf); hc= colorbar('location','eastoutside'); geoshow('landareas.shp','FaceColor',[.5 .5 .5]); %call shapefile to display land masses in grey ylabel(hc, 'DO (ml/l)','FontSize',14); caxis([3 6]); subplot(2,1,2) axesm('MapProjection','mercator','MeridianLabel','on','ParallelLabel',... 'on','mlinelocation', 20,'plinelocation',5,'mlinelocation',5,... 'maplatlimit',[17 35],'maplonlimit',[-100 -80],'grid' ,'on'); framem hold on; hidem(gca); %Hides rectangle border around map set(gcf,'color','w') %Background color of the figure to white surfm(temp_lat, temp_lon, temp_mean_surf); hc= colorbar('location','eastoutside'); geoshow('landareas.shp','FaceColor',[.5 .5 .5]); %call shapefile to display land masses in grey ylabel(hc, 'SST (Degrees C)','FontSize',14); caxis([15 33]); saveas(gcf,'DO_SST_annual.pdf'); %save current figure as "DO_SST_annual.pdf" %% Mapping mean Winter DO and SST figure subplot(2,1,1) load coast axesm('MapProjection','mercator','MeridianLabel','on','ParallelLabel',... 'on','mlinelocation', 20,'plinelocation',5,'mlinelocation',5,... 'maplatlimit',[17 35],'maplonlimit',[-100 -80],'grid' ,'on');

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framem hold on; hidem(gca); %Hides rectangle border around map set(gcf,'color','w') %Background color of the figure to white surfm(DO_lat,DO_lon,DO_winter); hc= colorbar('location','eastoutside'); geoshow('landareas.shp','FaceColor',[.5 .5 .5]); %call shapefile to display land masses in grey ylabel(hc, 'DO (ml/l)','FontSize',14); caxis([4 5]); subplot(2,1,2) axesm('MapProjection','mercator','MeridianLabel','on','ParallelLabel',... 'on','mlinelocation', 20,'plinelocation',5,'mlinelocation',5,... 'maplatlimit',[17 35],'maplonlimit',[-100 -80],'grid' ,'on'); framem hold on; hidem(gca); %Hides rectangle border around map set(gcf,'color','w') %Background color of the figure to white surfm(temp_lat, temp_lon, temp_winter); hc= colorbar('location','eastoutside'); geoshow('landareas.shp','FaceColor',[.5 .5 .5]); %call shapefile to display land masses in grey ylabel(hc, 'SST (Degrees C)','FontSize',14); caxis([27 30]); saveas(gcf, 'DO_SST_winter.pdf'); %save current figure as "DO_SST_winter.pdf" %% Mapping mean Summer DO and SST figure subplot(2,1,1) load coast axesm('MapProjection','mercator','MeridianLabel','on','ParallelLabel',... 'on','mlinelocation', 20,'plinelocation',5,'mlinelocation',5,... 'maplatlimit',[17 35],'maplonlimit',[-100 -80],'grid' ,'on'); framem hold on; hidem(gca); %Hides rectangle border around map set(gcf,'color','w') %Background color of the figure to white surfm(DO_lat,DO_lon,DO_summer); hc= colorbar('location','eastoutside'); geoshow('landareas.shp','FaceColor',[.5 .5 .5]); %call shapefile to display land masses in grey ylabel(hc, 'DO (ml/l)','FontSize',14); caxis([3 6]); subplot(2,1,2) axesm('MapProjection','mercator','MeridianLabel','on','ParallelLabel',... 'on','mlinelocation', 20,'plinelocation',5,'mlinelocation',5,... 'maplatlimit',[17 35],'maplonlimit',[-100 -80],'grid' ,'on'); framem hold on; hidem(gca); %Hides rectangle border around map set(gcf,'color','w') %Background color of the figure to white surfm(temp_lat, temp_lon, temp_summer);

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hc= colorbar('location','eastoutside'); geoshow('landareas.shp','FaceColor',[.5 .5 .5]); %call shapefile to display land masses in grey ylabel(hc, 'SST (Degrees C)','FontSize',14); caxis([15 33]); saveas(gcf, 'DO_SST_summer.pdf'); %save current figure as "DO_SST_winter.pdf" %% Finding differences between Winter and Summer SST and DO % I used indexing to find the parts of the DO_clim that matter (GOM area) %Subset a small area of the Gulf of Mexico where DO and SST changes were %more dramatic (i.e, inshore near output of Mississippi River) %Subset are surface measurements from 27.5-20.5 degrees N and 85.5-88.5 degrees W GOM_surf_DO_inshore = DO_clim(272:275,118:121,1,:); GOM_surf_temp_inshore = temp_clim(272:275,118:121,1,:); % Averaging DO over Latitude and Longitude GOM_DO_subset_inshore = squeeze(nanmean(nanmean(GOM_surf_DO_inshore,1),2)); GOM_temp_subset_inshore = squeeze(nanmean(nanmean(GOM_surf_temp_inshore,1),2)); months = [1:12]; %#ok %create time vector (x). %This vector is the same as the DO_time and temp_time vectors, just in an easier format to plot. %Subset a small area of the Gulf of Mexico where DO and SST changes were %less dramatic (i.e. middle of the Gulf) %Subset are surface measurements from 23.5-26.5 degrees N and 87.5-90.5 degrees W %Just subsetting the surface for all months GOM_surf_DO_middle = DO_clim(270:273,114:117,1,:); GOM_surf_temp_middle = temp_clim(270:273,114:117,1,:); % Averaging DO over Latitude and Longitude GOM_DO_subset_middle = squeeze(nanmean(nanmean(GOM_surf_DO_middle,1),2)); GOM_temp_subset_middle = squeeze(nanmean(nanmean(GOM_surf_temp_middle,1),2)); %% Plotting annual DO and SST differences at the surface figure; subplot(2,2,1); plot(months,GOM_DO_subset_inshore(:,1),'.k-'); xlabel('Month'); xlim([1 12]); ylabel('Inshore DO (ml/l)'); ylim([4 5.5]); set(gcf,'color','white'); suptitle('Annual Surface DO and SST'); subplot(2,2,2); plot(months,GOM_DO_subset_middle(:,1),'.k-'); xlabel('Month');

[NAME REMOVED]– EOS 321 xlim([1 12]); ylabel('Offshore DO (ml/l)'); ylim([4 5.5]); set(gcf,'color','white'); subplot(2,2,3); plot(months,GOM_temp_subset_inshore(:,1),'.b-'); xlabel('Month'); xlim([1 12]); ylabel('Inshore Temperature (degrees C)'); ylim([20 30]); set(gcf,'color','white'); subplot(2,2,4); plot(months,GOM_temp_subset_middle(:,1),'.b-'); xlabel('Month'); xlim([1 12]); ylabel('Offshore Temperature (degrees C)'); ylim([20 30]); set(gcf,'color','white'); saveas(gcf,'Annual_DO_SST.pdf'); %save current figure as "Annual_DO_SST" %% Looking in the same subset regions at how DO and SST change with depth. %Subset a small area of the Gulf of Mexico where DO and SST changes were %less dramatic (i.e. middle of the Gulf) %Subset are surface measurements from 23.5-26.5 degrees N and 87.5-90.5 degrees W %Subsetting Winter and Summer at all depths. Jan_depth_DO_middle = DO_clim(270:273,114:117,:,[1,2,12]); Jan_depth_temp_middle = temp_clim(270:273,114:117,:,[1,2,12]); Jul_depth_DO_middle = DO_clim(270:273,114:117,:,6:8); Jul_depth_temp_middle = temp_clim(270:273,114:117,:,6:8); Jan_depth_DO_inshore = DO_clim(272:275,118:121,:,[1,2,12]); Jan_depth_temp_inshore = temp_clim(272:275,118:121,:,[1,2,12]); Jul_depth_DO_inshore = DO_clim(272:275,118:121,:,6:8); Jul_depth_temp_inshore = temp_clim(272:275,118:121,:,6:8); % Averaging DO over Latitude, Longitude, and Season Jan_DO_depth_inshore_av = squeeze(nanmean(nanmean(nanmean(Jan_depth_DO_inshore,1),2),4)); Jan_temp_depth_inshore_av = squeeze(nanmean(nanmean(nanmean(Jan_depth_temp_inshore,1),2),4)); Jan_DO_depth_middle_av = squeeze(nanmean(nanmean(nanmean(Jan_depth_DO_middle,1),2),4)); Jan_temp_depth_middle_av = squeeze(nanmean(nanmean(nanmean(Jan_depth_temp_middle,1),2),4)); Jul_DO_depth_inshore_av = squeeze(nanmean(nanmean(nanmean(Jul_depth_DO_inshore,1),2),4)); Jul_temp_depth_inshore_av = squeeze(nanmean(nanmean(nanmean(Jul_depth_temp_inshore,1),2),4)); Jul_DO_depth_middle_av = squeeze(nanmean(nanmean(nanmean(Jul_depth_DO_middle,1),2),4)); Jul_temp_depth_middle_av = squeeze(nanmean(nanmean(nanmean(Jul_depth_temp_middle,1),2),4));

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[NAME REMOVED]– EOS 321

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%% Plotting depth changes in subset regions in January and July % Plotting Inshore Region first figure; suptitle('DO and Temperature Depth Profiles'); subplot(2,2,1); plot(Jan_DO_depth_inshore_av,DO_depth,'b.-'); % Jan Inshore DO depth profile hold on plot(Jul_DO_depth_inshore_av,DO_depth,'r.-'); %July depth profile set(gca,'ydir','reverse') %0 is at top surface and increases w depth ylabel('Depth (m)'); xlabel('Inshore DO (ml/l)'); legend('Winter','Summer'); legend('Location','Southwest'); set(gcf,'color','white'); xlim([2 6]); subplot(2,2,2); plot(Jan_temp_depth_inshore_av,temp_depth,'b.-'); %January temp depth profile hold on plot(Jul_temp_depth_inshore_av,temp_depth,'r.-'); %July temp depth profile set(gca,'ydir','reverse'); %0 is at top surface and increases w depth ylabel('Depth (m)'); xlabel('Inshore Temperature (Degrees C)'); legend('Winter','Summer'); legend('Location','Southeast'); %Plotting Offshore Region subplot(2,2,3); plot(Jan_DO_depth_middle_av,DO_depth,'b.-'); % Jan Inshore DO depth profile hold on plot(Jul_DO_depth_middle_av,DO_depth,'r.-'); %July depth profile set(gca,'ydir','reverse') %0 is at top surface and increases w depth ylabel('Depth (m)'); xlabel('Offshore DO (ml/l)'); legend('Winter','Summer'); legend('Location','Southwest'); set(gcf,'color','white'); xlim([2 6]); subplot(2,2,4); plot(Jan_temp_depth_middle_av,temp_depth,'b.-'); %January temp depth profile hold on plot(Jul_temp_depth_middle_av,temp_depth,'r.-'); %July temp depth profile set(gca,'ydir','reverse'); %0 is at top surface and increases w depth ylabel('Depth (m)'); xlabel('Offshore Temperature (Degrees C)'); legend('Winter','Summer'); legend('Location','Southeast'); saveas(gcf,'DO_Temp_Depth_Profiles.pdf');