Ocean In Winter Research Articles

Mid-depth recirculation observed in the interior Labrador and Irminger seas by direct velocity measurements

The Labrador Sea is one of the sites where convection exports surface water to the deep ocean in winter as part of the thermohaline circulation. Labrador Sea water is characteristically cold and fresh, and it can be traced at intermediate depths (500-2,000 m) across the North Atlantic Ocean, to the south and to the east of the Labrador Sea. Widespread observations of the ocean currents that lead to this distribution of Labrador Sea water have, however, been difficult and therefore scarce. We have used more than 200 subsurface floats to measure directly basin-wide horizontal velocities at various depths in the Labrador and Irminger seas. We observe unanticipated recirculations of the mid-depth (approximately 700 m) cyclonic boundary currents in both basins, leading to an anticyclonic flow in the interior of the Labrador basin. About 40% of the floats from the region of deep convection left the basin within one year and were rapidly transported in the anticyclonic flow to the Irminger basin, and also eastwards into the subpolar gyre. Surprisingly, the float tracks did not clearly depict the deep western boundary current, which is the expected main pathway of Labrador Sea water in the thermohaline circulation. Rather, the flow along the boundary near Flemish Cap is dominated by eddies that transport water offshore. Our detailed observations of the velocity structure with a high data coverage suggest that we may have to revise our picture of the formation and spreading of Labrador Sea water, and future studies with similar instrumentation will allow new insights on the intermediate depth ocean circulation.

Use of otolith microstructure to study life history of juvenile chinook salmon in the Strait of Georgia in 1995 and 1996

The pattern of otolith daily increments was used to identify hatchery-reared, wild ocean-type and wild stream-type chinook and study their life history in the Strait of Georgia. In 1995 and 1996, almost all of hatchery-reared and wild stream-type chinook entered the Strait of Georgia in May and June, while wild ocean-type chinook entered from April to August. Upon ocean entry stream-type fish were the largest and wild ocean-type the smallest. Hatchery-reared and wild ocean-type chinook leaving fresh water later in the year were larger than those leaving earlier. The mean length of wild stream-type chinook was not related to the time of ocean entry. All the life history types maintained their size differences throughout the summer and fall despite some differences in rates of size increase. Hatchery-reared and wild stream-type chinook grew faster in 1995 than in 1996. Wild ocean-type grew at about the same rate. During early summer, the percentage of wild ocean-type chinook was low in contrast to the percentage of hatchery-reared and wild stream-type chinook in 1995 and 1996, respectively. In September of both years, the percentage of wild ocean-type chinook increased and the percentage of hatchery-reared and wild stream-type chinook dropped. By November in both years, the percentage of hatchery-reared chinook increased, especially in 1996 when the percentage exceeded 80%. After the first ocean winter, the percentage of hatchery-reared fish remained high.

A modeling study of upper ocean winter processes in the Labrador Sea

A coupled ice‐mixed layer model is developed to study winter processes in the Labrador Sea. The seasonal change of mixed‐layer properties, air‐sea fluxes, and ice coverage is examined. The effects of severe atmospheric conditions and salinity change on the upper ocean are investigated. The model is integrated from November to June to cover the entire winter period. Objectively analyzed temperature and salinity fields for November are used as the initial conditions of the model ocean. Meteorological parameters derived from the NCEP reanalysis are used as forcings. The results show that heat loss of the ocean reaches a maximum at the end of January. High heat loss, 250 to 400 W m−2, occurs in the northern Labrador Sea between 56°N and 63°N in ice‐free waters near the ice edge. Pack ice significantly reduces the heat loss with a typical value of 50 W m−2. In the northern Labrador Sea, surface cooling causes the mixed layer to deepen continuously through winter and reaches a maximum of 150–450 m in late March. A decrease of surface salinity by 1% (for example, from 34.35 to 34) results in a decrease of mixed‐layer depth by 17–55%. The high stratification associated with the low surface salinity has little effect on ice coverage, since the reduced level of vertical mixing cannot lower the surface temperature sufficiently to increase the ice area. This suggests that freshening of the Labrador Sea during the Great Salinity Anomaly in the late 1960s to early 1970s did not promote ice production. An increase of wind speed by 40% and a decrease of air temperature up to 4°C, representing the conditions of cold winters, doubles the mixed‐layer depth to a maximum of 900 m and extends the southern ice limit by 200 km on the northern Grand Banks. This suggests that interannual variation of convection and ice extent are mainly controlled by local meteorological conditions.

North Brazil current: vertical structure

On the basis of the data ofin situ measurements of the velocities of currents and basic hydrophysical parameters (such as temperature and salinity) carried out during Cruise 41 of the R/VAkademik Vernadsky, we analyze the structure of the North Brazil Current near the continental slope and in the equatorial abyssal part of the ocean in winter, establish the regularities of changes in the current velocity with depth, and compare the structures of the North Brazil and Guiana Currents.

Estimating late-winter heat flow to the atmosphere from the lake-dominated Alaskan North Slope

AbstractThe conductive heat flux through the snow cover (Fa) is used as a proxy to examine the hypothesis that there is a significant heat flow from the Alaskan North Slope to the atmosphere because of the large number of lakes in the region.Fais estimated from measurements of snow depth, temperature and density on tundra, grounded ice and floating ice in mid-April 1997 at six lakes near Barrow, northwestern Alaska. The meanFavalues from tundra, grounded ice and floating ice are 1.5, 5.4 and 18.6 W m2, respectively. A numerical model of the coupled snow/ice/water/soil system is used to simulateFaand there is good agreement between the simulated and measured fluxes. The flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn. The flux from the floating ice is high because the ice has a relatively high thermal conductivity, and a body of relatively warm water remains below the growing ice at the end of winter. The flux from the grounded ice is intermediate between that from the tundra and that from the floating ice, and depends on the timing of the contact between the growing ice and the lake sediments, and whether or not those sediments freeze completely. Using the estimatedFavalues combined with the areal fractions of tundra, grounded ice and floating ice derived from synthetic aperture radar images, area-weightedFavalues are calculated for six areas.Favalues for the ice vary between 9.8 and 13.8 W m−2, and those from the ice plus tundra vary between 3.9 and 5.3 W m−2. TheFavalues are similar to those observed in the sea-ice-covered regions of the south and north polar oceans in winter. The North Slope of Alaska may thus make a significant contribution to the regional energy budget in winter.

Estimating late-winter heat flow to the atmosphere from the lake-dominated Alaskan North Slope

AbstractThe conductive heat flux through the snow cover (Fa) is used as a proxy to examine the hypothesis that there is a significant heat flow from the Alaskan North Slope to the atmosphere because of the large number of lakes in the region. Fa is estimated from measurements of snow depth, temperature and density on tundra, grounded ice and floating ice in mid-April 1997 at six lakes near Barrow, northwestern Alaska. The mean Fa values from tundra, grounded ice and floating ice are 1.5, 5.4 and 18.6 W m2, respectively. A numerical model of the coupled snow/ice/water/soil system is used to simulate Fa and there is good agreement between the simulated and measured fluxes. The flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn. The flux from the floating ice is high because the ice has a relatively high thermal conductivity, and a body of relatively warm water remains below the growing ice at the end of winter. The flux from the grounded ice is intermediate between that from the tundra and that from the floating ice, and depends on the timing of the contact between the growing ice and the lake sediments, and whether or not those sediments freeze completely. Using the estimated Fa values combined with the areal fractions of tundra, grounded ice and floating ice derived from synthetic aperture radar images, area-weighted Fa values are calculated for six areas. Fa values for the ice vary between 9.8 and 13.8 W m−2, and those from the ice plus tundra vary between 3.9 and 5.3 W m−2. The Fa values are similar to those observed in the sea-ice-covered regions of the south and north polar oceans in winter. The North Slope of Alaska may thus make a significant contribution to the regional energy budget in winter.

Estimating late-winter heat flow to the atmosphere from the lake-dominated Alaskan North Slope

AbstractThe conductive heat flux through the snow cover (Fa) is used as a proxy to examine the hypothesis that there is a significant heat flow from the Alaskan North Slope to the atmosphere because of the large number of lakes in the region. Fa is estimated from measurements of snow depth, temperature and density on tundra, grounded ice and floating ice in mid-April 1997 at six lakes near Barrow, northwestern Alaska. The mean Fa values from tundra, grounded ice and floating ice are 1.5, 5.4 and 18.6 W m2, respectively. A numerical model of the coupled snow/ice/water/soil system is used to simulate Fa and there is good agreement between the simulated and measured fluxes. The flux from the tundra is low because the soils have a relatively low thermal conductivity and the active layer cools significantly after freezing completely the previous autumn. The flux from the floating ice is high because the ice has a relatively high thermal conductivity, and a body of relatively warm water remains below the growing ice at the end of winter. The flux from the grounded ice is intermediate between that from the tundra and that from the floating ice, and depends on the timing of the contact between the growing ice and the lake sediments, and whether or not those sediments freeze completely. Using the estimated Fa values combined with the areal fractions of tundra, grounded ice and floating ice derived from synthetic aperture radar images, area-weighted Fa values are calculated for six areas. Fa values for the ice vary between 9.8 and 13.8 W m−2, and those from the ice plus tundra vary between 3.9 and 5.3 W m−2. The Fa values are similar to those observed in the sea-ice-covered regions of the south and north polar oceans in winter. The North Slope of Alaska may thus make a significant contribution to the regional energy budget in winter.

Interannual variability in nitrate supply to surface waters of the Northeast Pacific Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 170:15-23 (1998) - doi:10.3354/meps170015 Interannual variability in nitrate supply to surface waters of the Northeast Pacific Ocean F. A. Whitney1,*, C. S. Wong1, P. W. Boyd2 1Institute of Ocean Sciences, PO Box 6000, Sidney, British Columbia V8L 4B2, Canada 2University of Otago, Dunedin, New Zealand *E-mail: whitneyf@dfo-mpo.gc.ca ABSTRACT: In the past decade, the upper ocean in the NE Pacific has undergone changes in physical and chemical properties which are similar to the recent El Niño/La Niña cycle. During the 1989 La Niña, winter waters at Ocean Station Papa (OSP) were relatively cool, saline and nitrate rich. With the onset of the 1991 El Niño period, however, winter waters at OSP were more saline by 0.3 psu, warmer by over 2°C and nitrate depleted by 30%. In 1994, oceanic winter temperatures were the warmest ever observed in over 40 yr of sampling. The decrease in winter nutrient supply persisted eastward from OSP to the coast of Vancouver Island, and resulted in an expanded area of nitrate depletion in summer. Lower winter nitrate supply is estimated to have reduced new production through spring and summer by 40% (2 million tonnes C) in a 290000 km2 patch of ocean west of Vancouver Island. We suggest that declines in phytoplankton production of this magnitude affect both the productivity and composition of higher trophic levels. KEY WORDS: Northeast Pacific · Alaskan Gyre · Mixed layer · Nitrate · Temperature · Salinity · El Niño · New production · Interannual variability Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 170. Publication date: September 03, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Evidence for a winter sink of atmospheric carbonyl sulfide in the northeast Atlantic Ocean

Atmospheric and dissolved carbonyl sulfide (COS) concentrations were measured on 473 samples during three cruises into the northeast Atlantic Ocean. The cruises took place in April/May 1992, January 1994, and September 1994, covering three seasons. In January 1994, persistent undersaturation of COS in seawater with respect to the atmosphere was observed. This is the first data set to show a strong and persistent undersaturation with the mean saturation ratio (SR) being 46% and the standard deviation 13%. In April 1992, the seawater was slightly supersaturated, with a SR of 126±58 %. Only in September 1994, strong supersaturation of 214±86% was observed. The measured air concentrations were relatively uniform, averaging 410±67 pptv in January 1994, 466±42 pptv in April 1992, and 396±18 pptv in September 1994. Sea‐to‐air fluxes of COS were estimated using three different exchange models. We obtained moderate to low COS emissions in September (19 to 33 nmol m−2 d−1) and April/May (5 to 10 nmol m−2 d−1), in contrast to a significant flux from the atmosphere into the ocean in January (−76 to −31 nmol m−2 d−1). The strong seasonal variation of COS emissions with the possibility of reversed fluxes into the ocean during winter must be considered in future oceanic source estimates. The possible effect of an open ocean winter sink on global marine emissions of COS could be a reduction by some 10–15%.

Criteria for the evaluation of alternative environmental monitoring variables: Theory and an application using winter flounder (Pleuronectes americanus) and Dover sole (Microstomus pacificus)

The design of environmental monitoring programs is frequently hampered by a lack of objective, quantitative criteria for evaluating alternative monitoring variables. In this paper we describe two such criteria, which we call samples required - the number of samples required to detect a given change in value - and information imparted - the amount of environmental information revealed by the monitoring variable. We then use these criteria to evaluate fin erosion in winter flounder (Pleuronectes americanus) and Dover sole (Microstomus pacificus) as marine environmental monitoring variables. Two methods for determining the samples required use contaminated and reference areas to estimate the sample statistics of a hypothetical impacted population. The first method is based on the overall difference in the proportions of diseased fish in the reference and hypothetical populations. The second treats the proportion of diseased fish in individual trawls as the variate and determines the samples required based on the mean and variance of the reference and contaminated populations. We use both methods to predict the number of trawls needed to detect an increase of 200% in fin erosion in the reference population. The first method had greater statistical power but assumes spatially homogeneous populations. The second method accounts for environmental patchiness. For Dover sole it predicted 1661 trawls would be needed to detect the 200% increase. An estuarine winter flounder population would require 74 trawls, and an oceanic winter flounder population would require 142.5 trawls. It appears that fin erosion in winter flounder may be a useful indicator of environmental contamination, but several stipulations apply. Migration may inflate the number of diseased fish observed in the reference population, and a more detailed etiology of the disease is required, including an understanding of what contaminants are responsible for manifestation of the disease.

Episodic outflow of suspended sediments from the Kii Channel to the Pacific Ocean in winter

Episodic outflow of suspended sediments from the Kii Channel to the Pacific Ocean in winter was observed by the sediment traps experiment above the shelf slope. When the current speed was weak and its direction was south or southwestward above the shelf slope the sinking sediment flux was nearly zero but the sinking sediment flux increased to 22g m−2 day−1 after the current speed was strong, its direction changed to south-west or westward and water temperature fell. Such intermitten sinking sediment flux above the shelf slope is considered to be related to the intermittent intrusion of the turbid and cold shelf water into the sub-surface layer of the transparent and warm slope water. Such episodic events may play a very important role in the material transport from the coastal sea to the open ocean.

Thyroid hormone levels in Atlantic salmon (Salmo salar) during the return migration from the ocean to spawn

Serum thyroid hormone levels were determined in adult Atlantic salmon (Salmo salar) of both sexes caught in the ocean and at a sequence of locations on their return migration to spawn. Tri‐iodothyronine (T3) levels were greatest in fish caught in coastal or estuarine waters or in a river near head‐of‐tide. T3 levels were lower in fish caught in rivers throughout the angling season and lowest in those captured entering a tributary near spawning. Thyroxine (T4) levels were lowest in immature fish captured in the ocean in winter but raised in fish captured in spring; many of the latter group showed endocrine evidence of their becoming sexually mature. T4 levels were greatest in fish captured in coastal waters and progressively lower in fish captured in an estuary, near head‐of‐tide and in rivers. T4 levels in fish captured at tributary entry near spawning exceeded those in fish caught in rivers earlier in the year. In general, these data support the hypothesis that motor activity level in migrant fish is a determinant of thyroid status.

Thyroid hormone levels in Atlantic salmon (Salmo salar) during the return migration from the ocean to spawn

Serum thyroid hormone levels were determined in adult Atlantic salmon (Salmo salar) of both sexes caught in the ocean and at a sequence of locations on their return migration to spawn. Tri-iodothyronine (T3) levels were greatest in fish caught in coastal or estuarine waters or in a river near head-of-tide. T3 levels were lower in fish caught in rivers throughout the angling season and lowest in those captured entering a tributary near spawning. Thyroxine (T4) levels were lowest in immature fish captured in the ocean in winter but raised in fish captured in spring; many of the latter group showed endocrine evidence of their becoming sexually mature. T4 levels were greatest in fish captured in coastal waters and progressively lower in fish captured in an estuary, near head-of-tide and in rivers. T4 levels in fish captured at tributary entry near spawning exceeded those in fish caught in rivers earlier in the year. In general, these data support the hypothesis that motor activity level in migrant fish is a determinant of thyroid status.

Radon Concentration, Absorbed Dose Rate in Air and Concentration of Natural Radionuclides in Soil in the Osaka District of Japan

Radon concentrations in outdoor air at 18 sites in the Osaka district, in the central part of Japan's main island, were measured with electrostatic integrating radon monitors which were developed by Y. Ikebe et al of the Osaka survey centre as part of a nationwide survey of radon indoors and outdoors in Japan conducted by the National Institute of Radiological Science (S. and M. Abe and K. Fujitaka). The mean radon concentration in outdoor air during 2-month periods was measured over a period of a year and a half. In addition, the absorbed dose rate in air and the concentration of natural radionuclides in soil were measured at 40 sites in Osaka Prefecture which is located in the central part of the Osaka district using thermoluminescence dosemeters and with gamma ray spectrometry, respectively. Radon concentration in outdoor air showed a seasonal pattern, reaching its maximum during the winter and its minimum during the summer, but this variation was not significant at the coastal sites. It was concluded that this variation is correlated with a seasonal wind which blows from the continental interior to the ocean in winter and in the opposite direction in summer, as well as the geographical factors. Radon concentration in outdoor air in the Osaka district ranged from 0.6 to 17.9 Bq.m-3 and mean annual radon concentration in outdoor air at the 18 sites ranged from 2.7 to 6.9 Bq.m-3. It was discovered that radon concentration in outdoor air decreased with wind speed in both winter and summer. The absorbed dose rate in air ranged from 66 to 114 nGy.h-1, and the concentration of 226Ra in soil ranged from 20 to 60 Bq.kg-1 respectively.

The Vorticity Budget of the Hemispheres

The cyclonic vorticity budget of the hemispheres is investigated using the output of the CCC GCM and objective analyses for the FGGE period. Analysis of GCM output gives direct estimates of the “topographic” and “frictional” vorticity sources and sinks, which are generally otherwise unavailable. In a broad sense, vorticity flows from source regions associated with high mean sea level pressure to sink regions associated with low mean sea level pressure. Direct estimates of the topographic source/sink term show a strong vorticity source associated with drainage flow from the elevated cold Antarctic plateau in Southern Hemisphere winter and, the reverse situation, a strong vorticity source associated with upward motion over the elevated warm Tibetan plateau in Northern Hemisphere summer. Direct estimates of the frictional source/sink term show strongest values over oceans in winter and over portions of the hot continental land masses of the Northern Hemisphere in summer. In both cases the instability of the lower layers of the atmosphere means that there is a good frictional connection between the surface and the free atmosphere. The seasonality of this behavior is especially notable over the southern oceans. From the zonally averaged point-of-view there is an interesting duality in the vorticity budget of the Southern Hemisphere. An almost complete cancellation occurs between the vorticity flux associated with the upper branches of the meridional circulation and that associated with the transient eddies. The vorticity transport is thus accomplished by the lower branches of the meridional circulation. When the budget terms are vertically integrated, however, the vorticity flux associated with the upper and lower branches of the meridional circulation tends to cancel so that the result is completely dominated by the transient eddy term.

Evolution of the southern ocean winter mixed layer and sea ice: Open ocean deepwater formation and ventilation

An analytical model has been developed to describe the nature of the winter ocean/sea ice interaction in the southern ocean, to determine the principal processes responsible for maintaining stability in this marginally stable region, and to predict the response to changes in the external forcing and initial conditions. The model accurately describes the sparse winter observations and the general temporal evolution of the ice, mixed layer depth, and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth. A scale analysis and sensitivity study reveal the system parameter dependence. This indicates that the magnitude of entrainment is proportional to Fst/(h0∇S), where Fs is the external salt flux; h0, the depth of the winter mixed layer; and ∇S, the salinity gradient through the pycnocline. Thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads. A strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere. This limits the amount of ice growth possible and plays the principal role in maintaining the system stability, since the ice growth is required for destabilization through haline rejection during the growth process. The system is also sensitive to the large ratio of heat to salt in the pycnocline. This introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux, which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere. This moderates the ability to grow ice and drive further entrainment. The absolute strength of the salinity gradient, on the other hand, dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment. The effectiveness with which changes in these parameters (as well as several other external parameters) can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis.

Verification of NMC's Spectral Model Jet-Level Oceanic Winter Season Forecasts by Use of Aircraft Data

Verification of NMC's Spectral Model Jet-Level Oceanic Winter Season Forecasts by Use of Aircraft Data

Satellite climatological aspects of the “polar low” and “instant occlusion”

Middle resolution DMSP (Defense Meterological Satellite Program) visible and infrared imagery are analyzed in conjunction with surface and upper-air synoptic observations for two years' (1977, 1978/79) mid-season months (January, April, July, October) to derive synoptic climatological information on the “polar low” and “instant occlusion” phenomena. Polar-air vortices occur most frequently over the oceans in winter. Regional differences in the dominance of cloud signature sub-types confirm variations in the dynamics involved in polar-air cyclogenesis, as noted by previous workers. The “comma cloud” appears to occur more frequently in the North Pacific, while the spiraliform vortex predominates in the North Atlantic. The latter seems to be at least partly attributable to the effect of the eastern Arctic sea-ice boundary, as demonstrated by an analysis of imagery for two winters (D. J. F). each representative of an opposing mode of the North Atlantic Oscillation (1974/75. 1976/77). Composite synoptic “models” of polar lows reveal surface-pressure departures similar to those for cyclogenesis of the frontal wave type. However, a cold core and little vertical tilt distinguish the polar low in the mean. The “instant occlusion” exhibits surface-pressure departures that are deeper and comparable to the mature/dissipating stages of wave cyclone evolution. Spatial patterns of the upper-air anomalies associated with instant occlusions show two distinct vortices: one apparently derived from the polar low, the other from the incipient frontal wave with which it has merged. The seasonal and latitude-dependent cyclone intensity statistics (all types) are applied to the cloud vortex inventory of the North Atlantic-Europe sector for January 1979, The results support the role of the polar low as a synoptic indicator of anomalous winter circulation in the extratropics. DOI: 10.1111/j.1600-0870.1985.tb00442.x

Cyclogenesis in Polar Air Streams

Abstract Two case studies of cyclogenesis that occurred in polar air streams behind or poleward of major frontal bands are presented. Based on the results of the studies, and on other evidence, characteristics of the type of disturbance in question are described. The cyclones in polar air masses are generally of small dimension, being spaced at intervals of 1000–1500 km when they occur in multiple form. They form most often over the oceans in winter, originating in regions of low-level heating and enhanced convection and acquiring a comma-shaped cloud pattern as they mature. They are associated with well-developed baroclinity throughout the troposphere and are located on the poleward side of the jet stream in a region marked by strong cyclonic wind shear and by conditional instability through a substantial depth of the troposphere. Instability mechanisms for their formation are discussed. It is concluded that they are primarily a baroclinic phenomenon that owe their below average size to the effect that s...

冬季北太平洋の風浪について-II(日本航海学会第38回講演会)

The authors have already obtained the theoretical wave chart of North Pacific Ocean in winter, using Mollie Darbyshire & L. Draper's table with the data of the Weather Maps. But the analysis was to be risen by the superior wind. In this paper, the wave height, the wind velocity and the wave period of all directions are shown and compared them with the meteorological reports by ships.