Carbon Dioxide In Surface Waters Research Articles

The effects of nutrient enrichment on algae and macroinvertebrates in the everglades: A review

Over 400 metric tons of phosphorus and 12,000 metric tons of nitrogen flow annually into the northern part of the Everglades. Data describing the effects of nutrient enrichment, especially phosphorus, on algae and macroinvertebrates in the Everglades are reviewed and compared to our preliminary results. The Everglades is a harsh aquatic environment characterized by high summer temperatures (>35 C) and fluctuating, low oxygen conditions. In unenriched habitats, oxygen concentrations at the algae-water interface can vary from 200% supersaturation (approximately 30 mg/l) during the day to less than 3.0 mg/l at night. Although surface water carbon dioxide concentrations from nighttime respiration are depleted by noon of the following day, pH remains circumneutral because of high bicarbonate concentrations. Growths of cyanobacteria, often exceeding 6 cm in thickness, characterize unenriched open water habitats. Despite longstanding suggestions to the contrary, there is no evidence that the cyanobacterial mat is consumed by higher trophic levels. Annual net daily metabolism in unenriched habitats ranges from −0.065 to 2.01 g C m−2 d−1 with an average of 0.92 g C m−2 d−1. Previous reports concerning the effects of P enrichment on oxygen and macroinvertebrates are confounded by comparisons between habitats that differ with respect to hydroperiod, water depth, and macrophyte species composition in addition to nutrient loading. Nutrient enrichment causes disintegration of the abundant cyanobacterial mat and a shift in algal species composition and relative abundance. Annual primary production and algal biomass were 2.9 and 3.0× greater, respectively, in phosphorus enriched conditions compared to unenriched areas. Algal diversity, however, was not significantly different in enriched compared to unenriched habitats. Our preliminary analyses indicate that macroinvertebrate diversity and density are higher within enriched compared to unenriched areas if similar habitat types (submerged macrophyte beds) are sampled. Also, there is no evidence that “fish kills” caused by anaerobiosis occur with greater frequency in enriched compared to unenriched areas.

Surface water carbon dioxide in the southwest Indian sector of the Southern Ocean: a highly variable CO 2 source/sink region in summer

Measurements of partial pressure of carbon dioxide ( pCO 2), total dissolved inorganic carbon (TCO 2), total alkalinity (TA) and chlorophyll a (Chl a) have been made in surface water in the southwestern Indian sector of the Southern Ocean (20–85°E) in the austral summer (INDIVAT V cruise, January-February 1987). Between Antarctica and Africa, pCO 2 distribution was linked to the oceanic frontal zones and Chi a variations. The pCO 2 spatial structure was very close to that explored in summer 1967 in the same region but the pCO 2 differences between the ocean and the atmosphere were smaller in 1987 than 20 years ago. At all latitudes we found strongly contrasting surface pCO 2 characteristics between eastern (around 80°E) and western (around 25°E) regions; C02 sources were mainly in the west and CO 2 sinks in the east. South of 60°S, the contrast could be due to biological activity. Between 60°S and the Antarctic Polar Front, intensification of upwelling might be responsible for the higher pCO 2 values in the west.

Chemical oceanography of the Indian Ocean, north of the equator

Chemical oceanographic studies in the North Indian Ocean have revealed several interesting and unique features. These are caused by the diverse conditions prevailing in the area which include immense river runoff in the northeast (Bay of Bengal) and a large excess of evaporation over precipitation and runoff in the northwest (Arabian Sea, Persian Gulf and Red Sea), resulting in the formation of several low- and high-salinity water masses. The occurrence of coastal upwelling seasonally makes the region highly fertile, and the existence of Asian landmass, forming the northern boundary, prevents quick renewal of subsurface layers. Consequently, dissolved oxygen gets severely depleted below the thermocline and reducing conditions prevail at intermediate depths (ca. 150–1200m) resulting in the reduction of nitrate (denitrification). The North Indian Ocean may contribute up to 10% of the global marine denitrification. The “denitrified” nitrogen, when combined with the rate of photosynthetic production reaching below the euphotic zone, gives the average residence time of water between 75 and 1200m as 43–51 years. The inorganic nutrient concentrations in the subsurface layers are very high in close proximity of the euphotic zone. The two-layered circulation leads to an active recycling of nutrients. The presence of organic fractions of nitrogen and phosphorus in significant concentrations in the deep water suggest that oxidation of organic matter is incomplete even great depths. The relationships between the apparent oxygen utilization (AOU) and nutrients and the stoichiometric composition of organic matter, deduced from the oxidative ratios and by analysis of plankton, are not very different from other oceanic areas. Higher nutrients and lower oxygen concentrations occur in the bottom layer as compared to the overlying water column in deep waters of the Bay of Bengal and Arabian Sea, suggesting that considerable quantities of organic matter reach the deep-sea floor, probably as fecal pellets, and get oxidized in the bottom layer. Very high silicate concentrations occur in the bottom water, especially in the Arabian Sea, decreasing steadily southward, indicating the solution of diatomaceous sediments from the sea floor. The silicate-rich waters appear to move southward over the north-bound, silicate-poor bottom water, resulting in the occurrence of a deep silicate maximum. The calcium: chlorinity ratio in the North Indian Ocean is appreciably higher than the oceanic averages. This is probably due to: (1) a high rate of river runoff in relatively small area; and (2) excessive stripping of calcium at the surface associated with a high biological productivity and its subsequent addition and regeneration in the bottom waters. The upward flux of calcium appears to be higher than in other oceanic areas. Other major constituents investigated (fluoride and magnesium) do not show any anomally. The partial pressure of carbon dioxide in surface waters of the North Indian Ocean is higher than that in the atmosphere which results in a net flux of carbon dioxide from the sea to the atmosphere. Stagnation of intermediate layers, coupled with high organic productivity at the surface, results in high total carbon dioxide content at these levels. An increase in carbonate ion concentration occurs with depth in deep waters (>1000m). Calcite saturation depth varies from 1000 to 3000m, increasing proressively southward. The lysocline lies at about 4000m depth, while the carbonate critical depth is located at 4000–5100m. The lysocline appears to be related to the “critical carbonate ion concentration” of 90±5 μm kg −1.

Carbon dioxide in surface ocean waters: 4. Global distribution

The distribution of the partial pressure of carbon dioxide in surface waters of the Atlantic, Pacific, and Indian oceans has been determined from 24 months of continuous measurements obtained on oceanic expeditions of the Scripps Institution of Oceanography in all three oceans, supplemented by 9 months of similar measurements and 55 discrete analyses obtained on other expeditions in the Atlantic Ocean and near the west coast of South America. The data, most of which represent summer conditions, are displayed on a chart that is the first to be prepared for the world's oceans. In the Pacific and Atlantic oceans pronounced belts of high pressure appear near the equator. The Pacific belt is far more extensive than the Atlantic, but the patterns are similar and both are clearly defined. In the Indian Ocean during the northern summer the pressure diminishes southward from India to 30°S with no high-pressure belt near the equator. In the subtropicals of all oceans the pressure tends to be low except in coastal areas where upwelling occurs. In polar areas patterns appear to be more complicated and are uncertain because the data are too few to establish seasonal variability.

Radium-226 and Radon-222: Concentration in Atlantic and Pacific Oceans

Measurements of radon-222 in seawater suggest the following. The radium-226 content of surface water in both the Atlantic and Pacific oceans is uniformly close to about 4 x 10(-14) gram per liter. The deep Pacific has a concentration of radium-226 that is four times higher and the deep Atlantic a concentration twice as high as that of the surface. These distribution profiles can be explained by the same particle-settling rate for radium-226 from surface to depth for the two oceans and by a threefold longer residence time of water in the deep Pacific than in the deep Atlantic. The vertical distribution of the deficiency of radon-222 in the surface water of the northwest Pacific Ocean suggests a coefficient of vertical eddy diffusion as high as 120 square centimeters per second and a gas-exchange rate for carbon dioxide in surface water between 14 and 60 moles per square meter per year. Vertical profiles of the excess of radon-222 in near-bottom water of the South Atlantic give coefficients of vertical eddy diffusion ranging from 1.5 to more than 50 square centimeters per second.

Carbon dioxide in surface waters of the Pacific Ocean: 1. Measurements of the distribution

Direct measurements of carbon dioxide in surface waters of the Pacific Ocean from 30°N to 65°S indicate high concentration relative to atmospheric CO2 in a broad belt near the equator and approaching the coast of South America. Elsewhere the concentration has been generally found to be nearly in equilibrium with the atmosphere or somewhat lower.

Carbon dioxide in surface waters of the Pacific Ocean: 2. Calculation of the exchange with the atmosphere

From direct measurements of the concentration of carbon dioxide gas in the atmosphere and ocean water, the average rate of exchange of CO2 per unit pressure difference and area across the atmosphere-ocean boundary from 30°N to 30°S in the Pacific Ocean is estimated to be 18 moles/(cm2 atm yr). This figure agrees approximately with the global average value deduced from radiocarbon measurements and supports a belief that the measurements of CO2, upon which the new estimate depends, have been established with a fairly high degree of precision.