Oceanic Regimes Research Articles

Flow-through analysis of Al in seawater by fluorometric detection with the use of lumogallion

A flow-through analytical method has been developed for the determination of trace amounts of aluminum in seawater with the use of Lumogallion fluorometric detection. Because iron was selectively removed by passing the sample through an 8-quinolinol immobilized chelating resin column (MAF-8HQ), this method could be applied to samples collected at the hydrothermal oceanic regime. Several known organic complexing agents were studied as a model group to examine the effect of naturally occurring organic ligands on the detection of aluminum in seawater. The detection limit was 0.17 nM for 10 ml of sample. The standard deviation was 2.7% at 2 nM of aluminum. This method permitted the sensitive, precise, and rapid determination of subnanomolar Al in seawater without contamination onboard ship. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 274–282, 2000

Climate states and variability of Arctic ice and water dynamics during 1946?1997

Recently observed changes in the Arctic have highlighted the need for a better understanding of Arctic dynamics. This research addresses that need and is also motivated by the recent finding of two regimes of Arctic ice - ocean wind-driven circulation. In this paper, we demonstrate that during 1946-1997 the Arctic environmental parameters have oscillated with a period of 10-15 years. Our results reveal significant differences among atmosphere, ice, and ocean processes during the anticyclonic and cyclonic regimes in the Arctic Ocean and its marginal seas. The oscillating behaviour of the Arctic Ocean we call the Arctic Ocean Oscillation (AOO). Based on existing data and results of numerical experiments, we conclude that during the anticyclonic circulation regime the prevailing processes lead to increases in atmospheric pressure, in ice concentration and ice thickness, river runoff, and surface water salinity - as well as to decreases in air temperature, wind speed, number of storms, precipitation, permafrost temperatures, coastal sea level, and surface water temperature. During the cyclonic circulation regime the prevailing processes lead to increased air and water temperatures, wind speed, number of storms,open water periods, and to decreases in ice thickness and ice concentration, river runoff, atmospheric pressure, and water salinity. The two-climate regime theory may help answer questions related to observed decadal variability of the Arctic Ocean and to reconcile the different conclusions among scientists who have analysed Arctic data obtained during different climate states.

Carbon and nitrogen isotopic composition of sedimenting particulate material at Station Papa in the subarctic northeast Pacific

The δ 13 C and δ 15 N of sedimenting particulate organic matter (POM) collected biweekly by sediment trap at 3800 m at Ocean Station Papa (OSP: 50°N, 135°W) in the NE subarctic Pacific from 1982 to 1990 changed significantly on seasonal and annual time-scales. δ 13 C POM ranged from −25.3 to −22.0‰, and δ 15 N POM ranged from 0.24 to 7.75‰, over the entire period, isotopically depleted values occurring mainly in summer and heavier values occurring in winter. Extreme depletion in δ 13 C POM values also occurred in the winters of 1982–83 and 1988–89 and in the late summer of 1985; these were not matched by significant changes in δ 15 N POM . The changes in isotope ratios are related to the annual changes in settling particulate fluxes only in a general way; flux maxima in particulate organic carbon (POC) and particulate organic nitrogen (PON) occurred in mid- and late summer in most years, but there is not a one-to-one correlation between these changes and the isotope variations. In some years, the isotope ratios begin to changed before the summer increase in settling fluxes. A one-year record of sedimenting δ 13 C POM and δ 15 N POM (1989–90) at three depths (200, 1000 and 3800 m) at the same location showed a marked carbon isotope enrichment with depth, consistent with decomposition or/and food-chain enrichment during particle settling, but very small changes in the nitrogen isotope composition of the same particles, suggesting that C and N are released from sedimenting particles via different pathways. Suspended δ 13 C POM and δ 15 N POM values increased significantly with depth and were higher than those of sedimenting POM below the euphotic zone, suggesting that the two types of POM do not interact in deep water. Seasonal variations in surface temperature, irradiance, phytoplankton growth rate, species composition and carbon fixation pathways do not appear to be important controls of the observed changes in δ 13 C POM ; the increases in temperature, irradiance and phytoplankton growth rate in the summer months should lead to enriched δ 13 C POM values rather than the observed isotopically light values in this season. Likewise, the summer increase in the growth of diatoms should produce isotopically heavy particles in view of the reported 13 C -enrichment of this group, and this should be augmented by the decrease in [CO 2] (aq) due to the summer increase in surface temperature. Opposing these possible controls, the planktonic food chain becomes shorter in the spring/early summer months, probably due to the migration to the surface of copepodites and their direct grazing on phytoplankton, and this results in 13 C enrichment relative to the winter months when the food chain is more complex. The relationship between sedimenting δ 15 N POM and the macro-nutrients at OSP is complicated by the fact that ammonium and urea are important phytoplankton substrates, and generally more so than nitrate. The change from isotopically heavy winter values to lighter summer values begins before the major drawdown of the surface nitrate, and the observed change is opposite to that observed in other ocean regimes, probably because nitrate never reaches limiting levels in this High Nutrient Low Chlorophyll regime. The change of phytoplankton composition from winter to summer also should lead to 15 N -enrichment, the opposite of the trends observed. Finally, the changes in sedimenting δ 15 N POM at OSP do not appear to be related to phytoplankton growth rate. We conclude that the nitrogen isotopic signal in settling POM at OSP reflects seasonal changes in food-web structure, the simpler (shorter) spring/summer plankton community causing a smaller isotopic fractionation from the nutrient substrate to sedimenting POM.

Phytoplankton dynamics in the NE subarctic Pacific

Ocean Station Papa (OSP, 50°N 145°W) in the NE subarctic Pacific is characterised as high nitrate low chlorophyll (HNLC). However, little is known about the spatial extent of these HNLC waters or the phytoplankton dynamics on the basin scale. Algal biomass, production and size-structure data are presented from winter, spring and summer between 1992 and 1997 for five stations ranging from coastal to open-ocean conditions. The inshore stations (P04–P16) are characterised by the classical seasonal cycle of spring and late summer blooms (production >3 g C m −2 d −1), diatoms are not Fe-stressed, and growth rate is probably controlled by macronutrient supply. The fate of the phytoplankton is likely sedimentation by diatom-dominated spring blooms, with a pelagic recycling system predominating at other times. The offshore stations (P20/OSP) display low seasonality in biomass and production (OSP, mean winter production 0.3 g C m −2 d −1, mean spring/summer production 0.85 g C m −2 d −1), and are dominated by small algal cells. Low Fe availability prevents the occurrence of diatom blooms observed inshore. The main fate of phytoplankton is probably recycling through the microbial food web, with relatively low sedimentation compared to inshore. However, the supply of macro- and micro-nutrients to the coastal and open ocean, respectively, may vary between years. Variability in macro-nutrient supply to the coastal ocean may result in decreased winter reserve nitrate, summer nitrate limitation, subsequent floristic shifts towards small cells, and reduced primary production. Offshore, higher diatom abundances are occasionally observed, perhaps indicating episodic Fe supply. The two distinct oceanic regimes have different phytoplankton dynamics resulting in different seasonality, community structure and fate of algal carbon. These differences will strongly influence the biogeochemical signatures of the coastal and open-oceanic NE subarctic Pacific.

The effect of land‐surface feedbacks on the monsoon circulation

AbstractSummary the effects of feedbacks from land‐surface forcing on intraseasonal monsoon activity are studied by performing idealized sensitivity experiments with a general circulation model.In agreement with observations, the simulated intraseasonal monsoon activity is mainly described by irregular alternations of active spells and break spells associated with fluctuations of the Tropical Convergence Zone (TCZ) between a continental and an oceanic regime. In the model, the spatial characteristic of the intraseasonal monsoon variability is a robust feature which is primarily related to an internal mode of variability of the system, rather than to a response to land‐surface feedbacks. Experimentation indicates that the simulation of northward propagating events, related to transitions in the regime, does not require the inclusion of interactive surface hydrological processes. This suggests that the transitions are also mainly related to internal atmospheric dynamics.The temporal characteristics of the fluctuations between the two TCZ regimes, however, are influenced by an interactive surface. the low‐frequency intraseasonal monsoon variability is enhanced by hydrological surface feedbacks. When the surface interacts with the atmosphere, the active and break regimes of the monsoon are equally likely. In the absence of surface feedbacks, the probability distribution is modified and the changes depend on the land‐surface conditions imposed. the results show that the probability of a monsoon break exceeds that of an active phase when the imposed land‐surface conditions are based on climatological values for July. This asymmetry in the probability distribution affects intraseasonal monsoon variability. In turn, the time‐mean monsoon circulation, depending as it does on the statistics of the intraseasonal oscillations (such as frequency of occurrence and mean amplitude), is also modified by the surface feedbacks. It follows that the surface conditions play a role in the interannual predictability of the time‐mean monsoon.

Vertical distribution and potential sources of strong ligands for copper(II) in the North Pacific

Complexing ability of natural organic ligands in seawater was determined by an approach based on coordination chemistry, i.e., thermodynamic calculations of the conditional stability constants of remarkably stable copper(II) complexes of natural ligands, which were maintained against the ligand-exchange reaction with a large excess of ethylenediaminetetraacetic acid. There exist strong ligands with the conditional stability constant of log K’CuL > 14 at pH 5.71 and 4° C ubiquitously in non-living dissolved organic matter, concentrated from both coastal and oceanic regimes. This type of ligand was detected at most depths from surface to 1,000 m in the oceanic regimes. The same appraoch was applied to a sample of marine organism (phytoplankton) and the strong ligand class was found out in phytoplankton. It is suggested that phytoplankton may be one of potential sources for the strong ligand.

Stratigraphic record of an Atlantic‐type global tectonic cycle in the Palaeoproterozoic Ashburton Province of Western Australia

New descriptive and interpretive stratigraphic frameworks for the Ashburton (and Gascoyne) Province of the Capricorn Orogen are based on sequence stratigraphy. Two megasequences are recognised. A lower megasequence (Megasequence VIIIL) is interpreted to record the opening, to the northwest, of an Atlantic‐type ocean. Four supersequences record rift and thermal‐subsidence stages of a divergent continental margin, with north‐ or northeast‐trending ocean‐margin and northwest‐trending failed‐rift geometries. There is no evidence for a southern oceanic regime. Rather, the Gawler Craton of South Australia is interpreted to have lain to the southwest of the Pilbara Craton, such that the cratons were a contiguous divergent continental margin. An upper megasequence (Megasequence VIIIU) is interpreted to record the conversion of the divergent margin to a convergent (hinterland) margin during southeast‐dipping subduction. Eight supersequences are recognised. These record backarc, remnant‐ocean, retroarc‐satellite and indent‐linked hinterland basins. All the basins preserve the failed‐rift geometry. To the southwest, collision‐indentation of the hinterland (Pilbara‐Gawler) continent by an indenter (Yilgarn Craton) is interpreted to have begun during the remnant‐ocean stage. An east‐ to east‐southeast‐trending megashear between the Pilbara and Yilgarn Cratons is interpreted to have been the boundary transform fault on the northern margin of that indenter.

Climate states and variability of Arctic ice and water dynamics during 1946–1997

Recently observed changes in the Arctic have highlighted the need for a better understanding of Arctic dynamics. This research addresses that need and is also motivated by the recent finding of two regimes of Arctic ice - ocean wind-driven circulation. In this paper, we demonstrate that during 1946-1997 the Arctic environmental parameters have oscillated with a period of 10-15 years. Our results reveal significant differences among atmosphere, ice, and ocean processes during the anticyclonic and cyclonic regimes in the Arctic Ocean and its marginal seas. The oscillating behaviour of the Arctic Ocean we call the Arctic Ocean Oscillation (AOO). Based on existing data and results of numerical experiments, we conclude that during the anticyclonic circulation regime the prevailing processes lead to increases in atmospheric pressure, in ice concentration and ice thickness, river runoff, and surface water salinity - as well as to decreases in air temperature, wind speed, number of storms, precipitation, permafrost temperatures, coastal sea level, and surface water temperature. During the cyclonic circulation regime the prevailing processes lead to increased air and water temperatures, wind speed, number of storms,open water periods, and to decreases in ice thickness and ice concentration, river runoff, atmospheric pressure, and water salinity. The two-climate regime theory may help answer questions related to observed decadal variability of the Arctic Ocean and to reconcile the different conclusions among scientists who have analysed Arctic data obtained during different climate states.

The Concept of Ocean Governance: Evolution Toward the 21st Century and the Principle of Sustainable Ocean Use

The concept of ocean governance encompasses norms, institutional arrangements, and substantive policies. The new ocean regime, for which the Third United Nations Law of the Sea Conference was the midwife, is based on the 1982 United Nations Convention on the Law of the Sea, but the 1982 convention by itself was clearly insufficient to take the world community into the twenty-first century. It has been supplemented by Agenda 21 of the UN Conference on Environment and Development (UNCED) of 1992; the Global Programme of Action for the Protection of the Marine Environment from Land-Based Activities of 1995; and the United Nations Agreement on Straddling Fish Stocks and Highly Migratory Fish Stocks of 1995. Even with these additions the fabric of the new ocean regime is insufficient to confront the new challenges faced by human use of the marine environment. Present patterns of human utilization of the world ocean are not sustainable over an indefinite future. There is an urgent need to breathe life into the notion of ''sustainability" to make it into a fundamental norm of the new world ocean regime. This article explores what such an effort would require in terms of norms, institutional arrangements, and substantive policies.

Reproductive performance of female Steller sea lions: an energetics-based reproductive strategy?

We examined the reproductive performance of female Steller sea lions (Eumetopias jubatus) in order to evaluate the hypothesis that low pup production was associated with nutritional stress and to assess whether reduced birth rates could have been a factor in a recent large-scale decline in numbers. Nearly all (97%) sexually mature females were pregnant during early gestation. However, by late gestation, pregnancy rates had declined to 67 and 55% in the 1970s and 1980s, respectively, owing to reproductive failures. We found that body condition, as depicted by mass index and blubber index, had a positive effect on the probability that a female would be pregnant during late gestation. Age, age2, and lactation were also associated with pregnancy status during late gestation. These findings support the hypotheses that reproductive failures were associated with lowered nutritional status and that the resulting low birth rates were a proximate factor in the decline. We speculate that abortion is a part of the reproductive strategy of the female Steller sea lion that enhances overall reproductive performance during times of suboptimal nutrition. A major shift in oceanic regime occurred in the Gulf of Alaska during the late 1970s that resulted in a reduction of about 50% in the overall biomass of fishes and a shift in species composition. Prey resources may not have been adequate to successfully support the Steller sea lions' "energetically expensive" reproductive/foraging strategy during the period of our study.

On the representation of the Southern Ocean water masses in an ocean climate model

In global ocean general circulation models used for climate studies, the simulated global deep ocean temperature and salinity generally appear to be lower than that observed. This may be due to an insufficient representation of the cryosphere in such models because the deep ocean thermohaline properties are strongly determined by high‐latitude surface conditions. In this study, it is our aim to arrive at an improved simulation of polar water mass characteristics and distribution in the framework of an ocean climate model. As a step toward identifying the critical factors influencing the high‐latitude water masses, in particular those of the Southern Ocean, we have proceeded a series of sensitivity experiments with a global sea ice‐ocean model. Forcing Southern Ocean sea ice with daily instead of monthly fluctuating wind enhances brine release due to new‐ice formation, which leads to a more pronounced core of Lower Circumpolar Deep Water (LCDW) in the Antarctic oceanic regime. Wider Antarctic shelf topography improves the distribution and thickness of sea ice, simultaneously providing a brine reservoir on the shelf, which is a crucial ingredient in the formation process of Antarctic Bottom Water (AABW). As a consequence, the salinity on the Antarctic shelf is increased with depth as observed. Intense southeasterly katabatic winds play a significant role in increasing the salinity, mainly off east Antarctica. It is suggested that modeled Southern Ocean water mass properties are highly sensitive to the large scale and regional forcing of Antarctic sea ice as well as the model representation of the shelf topography, the width of which is crucial to reproducing the first‐order features of near‐boundary convection.

Global relationships of the inherent optical properties of the oceans

We have collected data during eight separate research cruises from open ocean to estuarine oceanic environments. Inherent optical property data collected during these cruises were incorporated into a large database totaling 1914 vertical samples. The range of each inherent optical property within this database spans over 2 orders of magnitude. Using this database, we examine the spectral relationships of each of the inherent optical properties based on the measurements made at 488 nm. The results of this study show that there are dependencies in the individual inherent optical properties (IOP) spectra that are linearly related. The information from the regression models is used to explain the linear dependencies observed in the global data set. A separate data set collected from a recent cruise is used to compare regional relationships with the global. The implication of this research is that over a diversity of oceanic regimes, there are fundamental, first‐order relationships in the individual IOP spectra. These relationships can provide an estimate of the individual IOP spectral relationships when no information about the IOP is available, as is often the case in ocean color remote sensing. More detailed models, however, may be necessary in order to more accurately predict the IOP spectral relationships on regional scales where the expected range of variability is small.

Stable phytoplankton community structure in the Arabian Sea over the past 200,000 years

Glacial to interglacial climate changes have been related to organic carbon cycling in oceanic surface waters1, and this possible link has led to the development of sedimentary tracers of past marine biological production. For example, sediment records of organic carbon2, opal3 and biogenic barium4 have been used to reconstruct past variations in production in different oceanic regimes, but these tracers cannot be used to discriminate between the relative contributions of different phytoplankton groups. Such a discrimination would provide greater insight into the operation of the biological ‘pump’ transporting material down out of surface waters, and into the possible influence of the structure of oceanic food chains on carbon fluxes. Several organic biomarker compounds have now been established for tracing the contribution of different planktonic groups to organic carbon in sediments5,6,7. Here we show that four such biomarkers—dinosterol, alkenones, brassicasterol and chlorins, which represent dinoflagellates, prymnesiophytes, diatoms and chlorophyll-producers, respectively—have concordant concentration maxima that coincide with organic carbon maxima over the past 200,000 years in a sediment core from the northeastern Arabian Sea. Not only do these organic tracers track changes in ocean production in this region, but the similar distributions of dinosterol and brassicasterol indicate that the relative contributions of the dominant members of the phytoplankton community (diatoms and dinoflagellates) to production were roughly uniform on timescales greater than 3,000–4,000 years over the past 200,000 years.

Nanoflagellates of the central California waters: taxonomy, biogeography and abundance of primitive, green flagellates (Pedinophyceae, Prasinophyceae)

Examination of whole mounts of cells prepared from samples collected off central California, September 1989, has led to the identification of 14 taxa of primitive green nanoflagellates from the Pedinophyceae (1 species) and the Prasinophyceae (13 species). Three of the prasinophyte taxa are new to science. The finding of these new taxa, provisionally identified as Prasinophyte “Point Sur” sp. 1, 2, 3, is important because it emphasizes the persistent, overall lack of knowledge of prasinophyte biodiversity, and also because these forms combine prasinophycean features in a unique way that ultimately may question the currently accepted taxonomic system. The abundance estimates suggest that prasinophytes are most numerous in coastal waters and are relatively absent from oceanic regimes.

Nitrogen isotope fractionation during nitrate, ammonium and urea uptake by marine diatoms and coccolithophores under various conditions of N availability

Stable isotopes of N provide a new approach to the study of algal production in the ocean, yet knowledge of the isotope fractionation (epsilon) in various oceanic regimes is lacking. Here we report large and rapid changes in isotope composition (delta(15)N) of 2 coastal diatoms and 2 clones (open and coastal) of a coccolithophore grown in the simultaneous presence of nitrate, ammonium and urea under varying conditions of N availability (i.e. N-sufficiency and N-starvation followed by N-resupply) and hence different physiological states, During N-sufficiency, the delta(15)N of particulate organic N (PON) was well reproduced, using a model derived from Rayleigh distillation theory, with constant epsilon similar to that for growth on each individual N source. However, following N-resupply, the variations in delta(15)N(PON) could be well explained only in the case of the open ocean Emiliania huxleyi, with epsilon similar to N-sufficient conditions. It was concluded that the mechanism of isotope fractionation changed rapidly with N availability for the 3 coastal clones. However, in the case of E. huxleyi isolated from the Subarctic Pacific Ocean, no evidence of a change in mechanism was found, suggesting that perhaps open ocean species can quickly recover from N-depleted conditions.

Midwater fishes and shrimps as competitors and resource partitioning in low latitude oligotrophic ecosystems

Ohgotrophic tropical-subtrop~cal oceanic regimes constitute the largest and most ancient ecosystem on earth, with these enormous areas being characterized by high faunal divers~ty. The stability and age of the ecosystem have enabled the evolution of many similar species niches where there is considerable overlap in niche parameters such as food and space, resulting in high species packing, especially in the epiand mesopelagic zones. Competition for limited resources undoubtedly exists and has been described by MacArthur (1972; Geographical ecology, Harper and Row, New York) as diffuse competition where each species is impacted by many other species sharing the environment. Most studies of resource partitioning in the oceanic pelagial have been restricted to specific taxonomic groups, such as copepods, fishes, shrimps, or cephalopods, and intergroup relationships have not been examined. The 2 dominant (numbers and blomass) components of low latitude m.id\vater rmcronekton communities, based on trawl catches, are flshes and shrimps, and the present study reveals that species from each of these 2 assemblages occur in the same feeding guilds and hence potentially compete for food resources. However, as additional niche parameters are included in the analysis, such as food size and predator vertical distribution, groups of species with matching niche characteristics become increasingly smaller. Results of this study suggest that as additional information on individual life histories is obtained, such as data on seasonahty of reproduction and population dynamics, the same pattern will emerge as we have found for fishes and shrimps considered separately, i.e. that resource partitioning occurs at the species level despite the pressures of diffuse intraand intergroup competition. This mininlizes competitive exclusion and enables the maintenance of a high-diversity fauna in resource-poor low latitude ecosystems.

Butyltins in sediments from Santa Monica and San Pedro basins, California

Butyltins have been measured for the first time in sediments from the deeper waters of the Santa Monica and San Pedro (SM/SP) basins of Southern California borderland. Core samples were collected from water depths ranging from 458 m in the shelf to 906 m in the central basin. Surficial and a few subsurface sections from selected cores were analyzed for butyltins. The dominant components are generally dibutyl and monobutyltins (DBT and MBT, respectively). Microbial degradation of Tributyltin (TBT, the most toxic of the butyltin species) to DBT and MBT during the long range transport to deeper basins, as well as a lack of continuing inputs of TBT in the present times could justify the butyltins signatures found in the region. The levels of butyltins are in the lower range (below detection level, <1, to 14 ng of Sn g −1) relative to nearshore sediments. However, the results demonstrate that the butyltins are, indeed, found even in the sediments of the central basins of the Southern California borderland suggesting that deeper global oceanic regimes need to be further investigated for these compounds.

Relations between interannual and intraseasonal monsoon variability as diagnosed from AMIP integrations

AbstractMonsoon variability on intraseasonal and interannual time‐scales is analysed using data from five 10‐year European Centre for Medium‐Range Weather Forecasts Atmospheric Model Intercomparison Project integrations, which differ only in their initial conditions. the results show that monsoon fluctuations within a season and within different years have a common dominant mode of variability. the spatial pattern of the common dominant mode in precipitation has a pronounced zonal structure, with one band of anomalous rainfall extending from 20°N to 5°N, covering most of the land areas, with the other band, of opposite sign, lying between 5°N and 10°S, mostly over the Indian Ocean. This mode therefore describes both the active/break monsoon spells associated with fluctuations of the Tropical Convergence Zone (TCZ) between the continental and the oceanic regime and the principal pattern of interannual variability of monsoon rainfall. In the observations the oscillations between active and break monsoon spells have similar behaviour, although the model is deficient in representing the rainfall variability over India.On the intraseasonal time‐scale the transition between the two regimes seems to have a chaotic nature. In addition the probability density function of the principal mode is bimodal for the years in which this mode is particularly dominant. These two results indicate a possible similarity with the Lorenz 3‐component chaotic model. Northward‐propagating convective regions, simulated by the model, are not clearly associated with the phase transitions of the TCZ regime. the timing of the monsoon onset appears to be modulated by the phase of the El Niño/Southern Oscillation during the preceding season, consistent with observational studies.The results suggest that the dominant mode may also represent some components of the observed monsoon variability. the interannual fluctuations of the dominant mode exhibit only a weak level of reproducibility compared with the relatively large predictability of a broad‐scale monsoon wind‐shear index.

Wind‐forced modeling studies of currents, meanders, and eddies in the California Current system

This process‐oriented study of the California Current system (CCS) uses a high‐resolution, multilevel, primitive equation ocean model on a β plane to isolate the response of that eastern boundary oceanic regime to temporal and spatially varying wind forcing. To study the generation, evolution, and maintenance of many of the observed features such as currents, meanders, and eddies in the CCS, the model is forced from rest with seasonal climatological winds. In response to the prevailing wind direction, surface equatorward currents develop, along with upwelling of cooler water along the coast and a poleward undercurrent. Baroclinic/barotropic instabilities in the equatorward surface current and poleward undercurrent result in the generation of meanders near the coast. As the meanders intensify, cold upwelling filaments develop along the coast and subsequently extend farther offshore. In time, the meanders form both cyclonic and anticyclonic eddies, which subsequently propagate farther offshore. Longer simulation times (∼3–4 years), in which a quasi‐equilibrium state for the CCS is reached, show a seasonal cycle in response to the wind forcing for the coastal currents, upwelling, and filaments. The meanders and eddies, however, can be quasi‐permanent as well as seasonal features. The quasi‐permanent features play a significant role in modifying coastal currents, upwelling, and filaments, which leads to large temporal and spatial variability in the CCS. In a sensitivity study, the results from several numerical experiments are used to examine the dependence of the generation of the currents, meanders, and eddies on the type of Coriolis parameterization, wind forcing, and coastline geometry. Both the meridional variability of ƒ(β plane) and the alongshore component of the wind stress are shown to be key ingredients for generating realistic vertical and horizontal structures for the cores of the surface equatorward and the subsurface poleward currents. With such structures the currents are baroclinically and barotropically unstable, resulting in the generation of meanders, filaments, and eddies. Irregularities in the coastline geometry are shown to be important for “anchoring” upwelling and filaments as well as for enhancing the growth of meanders and eddies. Cyclonic eddies tend to form in the vicinity of capes, while anticyclonic eddies tend to form in the coastal indentations between capes. The region off Cape Blanco is identified as the location where the coastal, equatorward flow off Oregon leaves the coast to develop a meandering jet off California. The results from these experiments support the hypothesis that wind forcing and coastline irregularities on a beta plane are important mechanisms for the generation of many of the observed features of the CCS.

Younger Dryas pollen records from Sverdrup Island (Kara Sea)

Sverdrup Island, in the Kara Sea, is currently occupied by polar desert vegetation. The analysis of Alleröd deposits indicates a climate drier than presently, with increased summer and decreased winter temperatures. The relative scarcity of distal pollen indicates that mainland source areas were located further south than at present. Younger Dryas cooling and increased dryness resulted in an increase of the proportions of Artemisia, Chenopodiaceae and Salix pollen, and in the extent of Sphagnum mosses. Preboreal time was marked by warmer, more humid conditions, with dwarf birches, Ericales and possibly Alnus fruticosa. The increased proportions of distally-derived arboreal birch pollen, coupled with the local component of the assemblages, indicates that the early Holocene represented the climatic optimum, initiated by the opening of the Arctic Ocean. Subsequent climate fluctuations were muted on Sverdrup Island, due to the development of microclimatic conditions associated with an oceanic regime.