Anomalous bottom water South of the grand banks suggests turbidity current activity

Highly turbid bottom water at the margin of the Sohm Abyssal Plain was identified by its temperature, salinity, and oxygen content as originating upslope on the continental rise. The fact that the particulate concentrations were one to two orders of magnitude higher than are normally found in deep ocean waters suggests a turbidity current as the agent bringing this water downslope.     

Temporal trends in deep ocean Redfield ratios

The Redfield ratio [carbon:nitrogen:phosphorus (C:N:P)] of particle flux to the deep ocean is a key factor in marine biogeochemical cycling. Changes in oceanic carbon sequestration have been linked to variations in the Redfield ratio on geological time scales, but this ratio generally is assumed to be constant with time in the modern ocean. However, deep-water Redfield ratios in the northern hemisphere show evidence for temporal trends over the past five decades. The North Atlantic Ocean exhibits a rising N:P ratio, which may be related to increased deposition of atmospheric nitrous oxides from anthropogenic N emissions. In the North Pacific Ocean, increasing C:N and C:P ratios are accompanied by rising remineralization rates, which suggests intensified export production. Stronger export of carbon in this region may be due to enhanced bioavailability of aeolian iron. These findings imply that the biological part of the marine carbon cycle currently is not in steady state.     

Beryllium-7 in ocean water

Concentration of the radio nuclide beryllium-7, produced by cosmic rays, was measured in waters collected from both the Atlantic and Pacific oceans. This short-lived nuclide is well suited as a tracer for interactions at the air-sea interface and for the measurement of rapid mixing processes in the surface layer of the ocean.     

The deep ocean during the last interglacial period

Oxygen isotope analysis of benthic foraminifera in deep sea cores from the Atlantic and Southern Oceans shows that during the last interglacial period, North Atlantic Deep Water (NADW) was 0.4 degrees +/- 0.2 degrees C warmer than today, whereas Antarctic Bottom Water temperatures were unchanged. Model simulations show that this distribution of deep water temperatures can be explained as a response of the ocean to forcing by high-latitude insolation. The warming of NADW was transferred to the Circumpolar Deep Water, providing additional heat around Antarctica, which may have been responsible for partial melting of the West Antarctic Ice Sheet.     

The ocean takes a deep breath

Deep convection is the major mechanism for replenishing oxygen in the deep interior of the world ocean, and its variability affects the use of atmospheric oxygen to monitor the global carbon cycle. Sensors mounted on autonomous floats allow this episodic breathing of the ocean to be monitored in near real time. The results suggest that the tools are available now to make oxygen a key parameter in marine global change research.     

Thermal structure of the deep pacific ocean in the early pliocene

The thermal structure of the Pacific Ocean between water depths of about 1 and 4.5 kilometers is estimated from the oxygen isotopic ratio of benthonic foraminifera from deep-drilled and piston cores of early Pliocene age (about 3 to 5 million years ago). The ratio of oxygen-18 to oxygen-16 in the early Pliocene at each site varies by an average of only +/- 0.12 per mil (1 standard deviation). A plot of the oxygen isotopic ratio against modern bottom-water temperature is adequately fit by a line having a slope of - 0.26 per mil per degree Celsius (the equilibrium temperature dependence of calcite-water fractionation), suggesting that the temperature gradient of the Pacific Ocean during the early Pliocene was similar to that of today.     

Polychlorobiphenyls in North Atlantic ocean water

Concentrations of polychlorobiphenyls (PCB's) have been measured at the surface and at various depths in the water of the North Atlantic Ocean between 26 degrees N and 63 degrees N. The concentrations average about 20 parts per trillion and amount to an estimated 2 x 10(4) metric tons of PCB's in the upper 200 meters of water. The average concentrations of PCB's in the surface water of the Sargasso Sea are lower than those in the northern North Atlantic.     

Climatic fluctuations due to deep ocean circulation

A simple climate model that includes the effect of deep ocean turnover as a pure time delay exhibits an oscillatory behavior. The deep ocean signal contains frequencies characteristic of both the forcing function and the deep ocean delay.     

Anomalous heat capacities of supercooled water and heavy water

Emulsification makes it possible to supercool water to the homogeneous nucleation temperature. Accordingly, the heat capacities of water and deuterium oxide have been determined from the respective equilibrium melting points to -38 degrees and to -34 degrees C, respectively. Two methods, drift calorimetry and differential scanning calorimetry, have been used. Both methods reveal a striking rise in the constant-pressure heat capacity below -20 degrees C. This indication of an apparently cooperative behavior should serve to test current theories of water, most notably perhaps, the pair potential model of Ben-Naim and Stillinger. Some implications of possible meteorological significance are mentioned.     

Anomalous water: characterization by physical methods

Anomalous water samples have been prepared in fused quartz capillaries from pure water in an unsaturated atmosphere. In agreement with observations of other investigators, water prepared in this manner, after concentration, exhibited an increased viscosity, a lowered vapor pressure, a phase separation at low temperatures, an index of refraction of 1.48 or greater, and a depression of the temperature of maximum density. However, electron microprobe examination indicated that a significant weight fraction of these concentrated anomalous water residues consists of sodium, boron, and oxygen. The presence of about 6 percent boron was also confirmed through neutron activation analyses and by mass spectrometric measurements. A parallel is drawn between the similar physical properties of anomalous water and highly concentrated sodium tetraborate solutions. The possibility of polymorphism in liquid water should be accepted only with serious reservations.     

Anomalous water: attempts at high-pressure synthesis

The high density, 1.4 grams per cubic centimeter, reported for anomalous water suggests that high pressures should be conducive to the formation of anomalous water. Six attempts at 60 kilobars in which water was cooled from about 600 degrees C in nickel or platinum tubes, with or without the presence of silica, did not produce any detectable amounts of anomalous water.     

Surface and deep ocean interactions during the cold climate event 8200 years ago

Evidence from a North Atlantic deep-sea sediment core reveals that the largest climatic perturbation in our present interglacial, the 8200-year event, is marked by two distinct cooling events in the subpolar North Atlantic at 8490 and 8290 years ago. An associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the Atlantic meridional overturning circulation. The existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying Laurentide Ice Sheet margin.     

Explosive deep water basalt in the sumisu backarc rift

Eruption of 1-million-year-old tholeiitic basalt >1800 meters below sea level (>18 megapascals) in a backarc rift behind the Bonin arc produced a scoriaceous breccia similar in some respects to that formed during subaerial eruptions. Explosion of the magma is thought to have produced frothy agglutinate which welded either on the sea floor or in a submarine eruption column. The resulting 135-meter-thick pyroclastic deposit has paleomagnetic inclinations that are random at a scale of <2.5 meters. High magmatic water content, which is about 1.3 percent by weight after vesiculation, contributed to the explosivity.     

The salinity,temperature, and delta18O of the glacial deep ocean

We use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from Ocean Drilling Program cores to reconstruct salinity and temperature of the deep ocean during the Last Glacial Maximum (LGM). Our data show that the temperatures of the deep Pacific, Southern, and Atlantic oceans during the LGM were relatively homogeneous and within error of the freezing point of seawater at the ocean's surface. Our chloride data show that the glacial stratification was dominated by salinity variations, in contrast with the modern ocean, for which temperature plays a primary role. During the LGM the Southern Ocean contained the saltiest water in the deep ocean. This reversal of the modern salinity contrast between the North and South Atlantic implies that the freshwater budget at the poles must have been quite different. A strict conversion of mean salinity at the LGM to equivalent sea-level change yields a value in excess of 140 meters. However, the storage of fresh water in ice shelves and/or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level.