Increase In Surface Water Temperature Research Articles

Increased thermohaline stratification as a possible cause for an ocean anoxic event in the Cretaceous period.

Ocean anoxic events were periods of high carbon burial that led to drawdown of atmospheric carbon dioxide, lowering of bottom-water oxygen concentrations and, in many cases, significant biological extinction. Most ocean anoxic events are thought to be caused by high productivity and export of carbon from surface waters which is then preserved in organic-rich sediments, known as black shales. But the factors that triggered some of these events remain uncertain. Here we present stable isotope data from a mid-Cretaceous ocean anoxic event that occurred 112 Myr ago, and that point to increased thermohaline stratification as the probable cause. Ocean anoxic event 1b is associated with an increase in surface-water temperatures and runoff that led to decreased bottom-water formation and elevated carbon burial in the restricted basins of the western Tethys and North Atlantic. This event is in many ways similar to that which led to the more recent Plio-Pleistocene Mediterranean sapropels, but the greater geographical extent and longer duration (approximately 46 kyr) of ocean anoxic event 1b suggest that processes leading to such ocean anoxic events in the North Atlantic and western Tethys were able to act over a much larger region, and sequester far more carbon, than any of the Quaternary sapropels.

Oceanic primary productivity and dissolved oxygen levels at the Cretaceous/Tertiary Boundary: Their decrease, subsequent warming, and recovery

Thirty‐six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the Cretaceous/Tertiary (K/T) boundary exposed at Caravaca, Spain. A rapid reduction in the gradient between δ13C values in fine fraction carbonate and benthic foraminiferal calcite and a decrease in the abundance of phosphorus (a proxy for organic carbon) and calcium were recorded in sediments 0–0.5 cm above the K/T boundary. These trends imply that an abrupt mass mortality occurred among pelagic organisms, leading to a significant reduction in the flux of organic carbon to the seafloor. In addition, variations in sulfur isotope ratios, the hydrocarbon‐generating potential of kerogen (measured as the hydrogen index), and foraminiferal indices of dissolved oxygen level all imply that a rapid decrease in dissolved oxygen was coincident with the δ13C event. Evidence of the low oxygen event has also been recognized in Japan and New Zealand, suggesting that intermediate water oxygen minima were widely developed during earliest Danian time. A threefold increase in the kaolinite/illite ratio and a 1.2‰ decrease in δ18O (carbonate fine fraction) were recorded in the basal 0.1–2 cm of Danian age sediments. These trends suggest that atmospheric warming and an increase in surface water temperature occurred 0–3 kyr after the δ13C event. Recovery in the difference between δ13C values in the carbonate fine fraction and in benthic foraminiferal calcite as well as increases in phosphorus and calcium contents occur at the base of planktonic foraminiferal Zone Pla, implying that an increase in primary productivity commenced some 13 kyr after the K/T boundary.Tables A1‐A3 are available on diskette or via Anonymous FTP from kosmos.agu.org directory APENO (Username = anonymous, Password = guest). Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009 or by phone at 800‐966‐2481; $15.00. Payment must accompany order.

Winter and spring evaluations of a wetland for tertiary wastewater treatment

The Union Electric Callaway Nuclear Power Plant currently uses a wetland that evolved after the retirement of a water treatment lagoon to supplement the existing mechanical wastewater treatment plant. The purpose of this study was to evaluate the wastewater treatment performance of the evolved wetland. Removal of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), ammonium, nitrate, phosphate, and sulfate were monitored during winter 1992 and early spring 1993. Hydraulic and hydrologic assessments were also conducted to determine the effective treatment area and actual detention times. The organic loading during the study was low, resulting in moderate decreases or increases in BOD, COD, TSS, and ammonium. The wetland system provided excellent reduction in phosphate, nitrate, and sulfate. Removal of all constituents was significantly greater during the early spring sampling period than the winter period. Increased performance was probably caused by increased surface water temperature, vegetative uptake, and greater detention times. A large amount of short circuiting was observed within the system, reducing detention time and wastewater treatment performance.

Late glacial-Holocene paleoclimatic and paleoceanographic evolution of the Aegean Sea: micropaleontological and stable isotopic evidence

Late glacial to Holocene paleoclimatic and paleoceanographic changes are examined using records of calcareous and organic-walled marine microfossils, pollen and terrestrial spores and oxygen isotope data in cores from the Aegean Sea basins. Planktic foraminiferal, coccolith and dinoflagellate data show that the late glacial-Holocene transition in the region was associated with a large warming of surface water. Mediterranean-based paleotransfer functions for planktic foraminifera show a 5 °–10 °C increase in surface water temperature from ~14,000 to ~9600 yr B.P. Estimates of surface water oxygen isotopic composition (δ18Ow) derived from planktic foraminiferal oxygen isotopic and transfer function data indicate that this warming was associated with a 2.0 to 2.5‰ reduction in δ18Ow. Transfer function results indicate corresponding 1.0 to 1.5‰ salinity reductions for this tim (ca. 6400–9600 yr B.P.) throughout the Aegean Sea. Pollen, dinoflagellate and isotopic data show that the early Holocene excess fresh water originated from rapid melting of the northern European and Siberian ice sheets, supplied primarily from the Black Sea by the opening of Bosphorus and Dardanelles Channels, during the post glacial sea-level rise, and supplemented by major rivers entering the Aegean Sea. Continuous outflow of fresh water into the Aegean Sea provided a low salinity surface lid, preventing the ventilation of the deep water. Benthic foraminifera shows a major turn-over that indicates low dissolved oxygen; however, bottom waters were not anoxic. Sapropel level S1 resulted from a combination of stagnant deep water in isolated depressions, increased terrigenous organic matter and periods of high primary productivity, as indicated by pollen and dinocysts, respectively. The surface water temperature and salinity reached present-day values at ~6400 yr B.P., with little subsequent change despite the major deforestation onshore.

An Introduction to Hurricanes in the Caribbean

THIS ISSUE OF BIOTROPICA brings together, for the first time, a collection of case studies that document the damage to natural ecosystems and the initial recovery process from three recent hurricanes in the Caribbean. The majority of papers address the impact of Hurricane Hugo (1989) and subsequent recovery during the year following the hurricane at three sites: St. John in the U.S. Virgin Islands, Puerto Rico, and South Carolina on the U.S. mainland (Fig. 1). Hurricane Hugo triggered a rapid increase in the level of hurricane research, in part because it passed over two Long-Term Ecological Research sites (Luquillo Experimental Forest, Puerto Rico and North Inlet, South Carolina) which had ecological data that allowed comparisons of prehurricane and posthurricane conditions. Benefits of such long-term studies include the ability to separate damage caused by the recent hurricane from previous damage; to not depend on reconstruction of damage scenarios from historical evidence; and, to begin studies of recovery immediately. Hurricane Hugo also provided an opportunity to contrast hurricane damage in different environments: tropical and temperate, humid and dry, island and continental. In addition to studies of Hurricane Hugo, we include studies of the effects of Hurricane Gilbert (1988) on Jamaica and Mexico, and Hurricane Joan (1988) on Nicaragua (Fig. 1). We have emphasized studies of terrestrial ecosystems; hurricane impacts on marine and coastal ecosystems have been examined elsewhere (Woodley et al. 1981, BenitoEspinal & Benito-Espinal 1991, Finkl & Pilkey 1991). Hurricanes are frequent, large-scale disturbances in the Caribbean. During the period 18711964, zero to eleven hurricanes per year (average = 4.6, median = 8) occurred in the Caribbean (Alaka 1976), resulting in, for example, a return time of 21 yr for the island of Puerto Rico (Salivia 1972). The strongest Caribbean hurricanes typically originate off the western coast of Africa, gain strength as they pass westward over the Atlantic Ocean, and rapidly deteriorate when they reach the mainland somewhere between Panama and New England. Weaker hurricanes and tropical storms (wind speeds 63-119 km/hr) have their origins throughout the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. With wind speeds of at least 119 km/hr and paths often tens of kilometers wide, hurricanes have a profound effect on plants, soils, animals, humans, and even landforms. Much attention is given to the destruction of property (Saffir 1991, Sparks 1991), and the loss of human lives in these storms. The effects of hurricanes on natural ecosystems (Fig. 2) have also been noted (e.g., Foster 1988) but are less understood. Studies in Puerto Rico suggest that hurricanes may have a major effect in structuring natural ecosystems in terms of age distribution of tropical forest trees (Doyle 1981, Weaver 1986, Lugo & Rivera-Batlle 1987), or biomass and species diversity (Crow 1980). These studies add to the accumulating evidence that suggests natural systems are largely organized by disturbance (Pickett & White 1985, Denslow 1987). The study of how natural ecosystems are altered by hurricanes and how they respond is essential to the understanding of how these systems are structured. Adding urgency to this study is the relationship between hurricanes and global climate change. Slight increases in surface water temperatures or periods of high rainfall in the I Received 28 July 1991, revision accepted 5 August 1991.

Paleotemperature and paleosalinity history of the estern Mediterranean during the Late Quaternary

Faunal and isotopic studies of continuous deep-sea cores were used to determine the paleotemperature and paleosalinity history of the eastern Mediterranean for the last 500,000 years. Temperature-related changes in the planktonic foraminiferal assemblages appear to be synchronous with glacial/interglacial changes in the open ocean. The oxygen isotopic records reveal fluctuations of up to 5%, much higher than the average open ocean glacial/interglacial amplitude. The abnormally high depletions in both 18O and 13C are consistently associated with sapropel layers and they are considered to be due to reduced surface salinities. The apparent phase difference between the isotopic and faunal records for stages 1–7 (last 250,000 years) does not represent real temporal leads or lags, but is due instead to regional salinity changes in the isotopic record superimposed on the global ice volume effect. A detailed study of Termination II (127,000 yr. B.P.) in a core east of Crete reveals a distinct set of paleoceanographic events associated with this rapid deglaciation. These include: (1) a rapid increase in surface water temperatures at about 127,000 yr. B.P.; (2) the deposition of sapropel D at about 125,000 yr. B.P.; (3) a localized increase in surface productivity also at 125,000 yr. B.P.; and (4) the return to normal open-marine conditions by about 120,000 yr. B.P.

Paleoceanographic events associated with termination II in the eastern Mediterranean : Thunell, R.C. and D.F. Williams, 1982. Oceanologica Acta, 5(2):229–233

Pelagie sedimentary sequences accumulating in the Mediterranean Sea provide a record of regional or localized paleoclimatic changes superimposed on broadscale global events. A sequence of paleoceanographic changes associated with the glacial/inter glacial transition at 127,000 years be fore present has been identified in the eastern Mediterranean Sea based on detailed microfossil and stable isotope studies. Specifically, these changes include a rapid increase in surface water temperature, the development of anoxie bottom conditions and a localized increase in productivity in the region around Crete. These events appear to be a response to the interplay of both a global warming at this time as weil as changes in drainage patterns in the circumMediterranean.