A three-species model explaining cyclic dominance of pacific salmon

The four-year oscillations of the number of spawning sockeye salmon (Oncorhynchus nerka) that return to their native stream within the Fraser River basin in Canada are a striking example of population oscillations. The period of the oscillation corresponds to the dominant generation time of these fish. Various - not fully convincing - explanations for these oscillations have been proposed, including stochastic influences, depensatory fishing, or genetic effects. Here, we show that the oscillations can be explained as a stable dynamical attractor of the population dynamics, resulting from a strong resonance near a Neimark Sacker bifurcation. This explains not only the long-term persistence of these oscillations, but also reproduces correctly the empirical sequence of salmon abundance within one period of the oscillations. Furthermore, it explains the observation that these oscillations occur only in sockeye stocks originating from large oligotrophic lakes, and that they are usually not observed in salmon species that have a longer generation time.Comment: 7 pages, 5 figure

A note on evanescent behavior of Arctic thermohaline intrusions

Temperature/salinity interleaving is a signature of thermohaline transition in the Arctic Ocean. These interleaving features, or intrusions, are observed to decrease in amplitude as they spread laterally from warmer toward cooler water. Here this phenomenon is investigated by considering the effect of a nonlinear equation of state on intrusion structure and behavior. The analysis shows that large-scale gradients of the thermal expansion coefficient (α) can induce a spatial decay of intrusion temperature, salinity, and velocity amplitudes toward cooler water. Spatial decay implies a recirculating flow between adjacent layers, which induces a slow vertical propagation of the intrusions. The temperature-dependence of α provides a mechanism which may act to trap intrusions in the vicinity of warm Arctic boundary currents, inhibiting ventilation of cooler waters

Water and Ice-Related Phenomena in the Coastal Region of the Beaufort Sea: Some Parallels between Native Experience and Western Science

Information gained through Native experience is combined here with scientific measurements to describe aspects of the wintertime oceanography of the Eskimo Lakes and Mackenzie River delta regions of the Canadian Beaufort Sea. The experiences of Jimmy Jacobson, a Tuktoyaktuk elder who lived in this region for over 70 years, were used as the basis for scientific planning and measurement. We focus on phenomena of special relevance to winter travel and fishing in four specific examples of Native insight guiding scientific inquiry. First, we examine local knowledge of ice characteristics and fish abundance in terms of tidal dispersion and its effect on mixing patterns during winter. Second, we relate the maintenance of a small ice-free area, used by caribou as a salt lick, to the vertical heat flux associated with flow through narrow channels. Third, we look at potentially dangerous episodes of overflooding of snow and ice in the nearshore zone in midwinter, caused by strong westerly winds, through the analysis of oxygen isotope distributions in ice cores. Fourth, we discuss the important influence of wind direction on ice conditions, lead formation, and brine production in semi-enclosed coastal bays. Finally, we note certain circulation features of ecological significance relevant to concerns about development and the transport of pollutants. We conclude that by not requiring agreement between indigenous knowledge and Western science, or ranking one above the other, we can realize the values of each approach. Specifically, indigenous knowledge can provide direction to scientific inquiry, while Western science can be used to measure, model, and predict where development or change might have the most serious impact.L’information acquise grâce à l’expérience des Autochtones est jumelée ici aux mesures scientifiques afin de donner lieu à la description des aspects de l’océanographie hivernale des régions des lacs Eskimo et du delta du fleuve Mackenzie dans la mer canadienne de Beaufort. L’expérience de Jimmy Jacobson, un ancien de Tuktoyaktuk qui habite dans la région depuis plus de 70 ans, a servi de fondement à la planification et aux mesures scientifiques. Nous nous concentrons sur les phénomènes qui revêtent une importance particulière dans le cadre des déplacements et de la pêche d’hiver de quatre exemples particuliers visant les perspectives autochtones ayant guidé l’enquête scientifique. Premièrement, nous examinons les connaissances locales pour ce qui est des caractéristiques propres à la glace et à l’abondance des poissons en termes de dispersion tidale et des effets sur les modèles de brassage pendant l’hiver. Deuxièmement, nous établissons un rapport entre le maintien de petites zones sans glace, dont les caribous se servent en guise de vasière, et le flux thermique vertical associé aux coureaux d’écoulement. Troisièmement, nous nous penchons sus des épisodes potentiellement dangereux de surinondation de neige et de glace dans la zone côtière en plein milieu de l’hiver, ce qui serait causé par de forts vents de l’ouest, en nous fondant sur l’analyse de la répartition des isotopes d’oxygène dans les carottes glaciaires. Quatrièmement, nous discutons de l’importante influence de l’orientation du vent sur le régime des glaces, la formation de filons et la production de saumure dans les baies côtières partiellement enfermées. En dernier lieu, nous faisons mention de certaines caractéristiques de circulation revêtant une importance écologique vis-à-vis des inquiétudes en matière de formation et de transport des polluants. Nous en concluons qu’en ne recherchant pas d’entente entre les connaissances des Autochtones et la science occidentale, ou qu’en accordant une préséance à l’une ou l’autre de ces notions, nous pouvons réaliser les valeurs de chaque approche. Plus précisément, les connaissances indigènes peuvent guider l’enquête scientifique, tandis que la science occidentale peut servir à mesurer, modéliser et prédire là où le développement ou le changement est susceptible d’avoir de plus grandes incidences

Oceanography of the Canadian Shelf of the Beaufort Sea: A Setting for Marine Life

Conservation of marine biodiversity in the Beaufort Sea demands that we understand what individual organisms require of their physical and geochemical environments in order to survive. Specifically, how do the extraordinary spatial and seasonal variations in ice cover, temperature, light, freshwater, turbidity, and currents of the Beaufort Sea define unique places or times critical to marine life? We start with the traditional "bottom-up" approach, which is to review the strongly seasonal physical forcing of the system, and from it to infer the resultant oceanographic regimes and seasons. This approach, while valuable, remains incomplete: this is due partly to limitations of the data and partly to our limited understanding of this complex system. The oceanographic features (e.g., upwelling regions, recurrent polynyas, coastal currents, sediment types and distributions) define the backdrop that animals "know and understand" in the sense of interacting with one another and finding food and habitat. We therefore seek clues to the underlying oceanographic processes in the behavioural patterns of fish, marine mammals, and birds. This "top-down" approach also has limitations, but it offers the opportunity to seek those connections in the system where climate change is likely to have its greatest impact on biological populations.La conservation de la biodiversité marine dans la mer de Beaufort passe par notre compréhension des éléments nécessaires à la survie des organismes individuels au sein de leur environnement physique et géochimique. En particulier, comment les variations spatiales et saisonnières extrêmes dans le couvert glaciel, la température, la lumière, l'eau douce, la turbidité et les courants de la mer de Beaufort définissent-elles des espaces uniques ou des périodes critiques à la vie marine? On commence avec l'approche traditionnelle "ascendante" qui consiste à examiner les pressions physiques largement saisonnières qui s'exercent sur le système, et on déduit les régimes et saisons océanographiques qui en découlent. Cette approche, tout en étant intéressante, reste incomplète, en partie à cause du manque de données et en partie à cause de notre compréhension insuffisante de ce système complexe. Les caractéristiques océanographiques (p. ex., les zones de remontée d'eau profonde, les polynies récurrentes, les courants côtiers, les types de sédiments et leur distribution) définissent l'arrière-plan que les animaux "connaissent et comprennent" au sens où ils y interagissent les uns avec les autres pour y trouver nourriture et habitat. On recherche par conséquent, dans les schémas de comportement des poissons, des mammifères marins et des oiseaux, des indices témoignant des processus océanographiques sous-jacents. Cette approche "descendante" a aussi ses limites, mais elle offre l'occasion de rechercher au sein du système les liens où le changement climatique est susceptible d'avoir le plus grand impact sur les populations biologiques

Combined effect of wind-forcing and isobath divergence on upwelling at Cape Bathurst, Beaufort Sea

Cape Bathurst is at the northeastern end of the Canadian Beaufort Shelf in the southeastern Beaufort Sea where the continental shelf abruptly ends at Amundsen Gulf. In this area, the steep slope east of the cape joins the relatively flat shelf immediately north of the cape leading to strong isobath divergence at the cape. Hydrographic and satellite data show upwelling of nutrient-rich, Pacific-origin water to the surface at Cape Bathurst when surface stress is upwelling-favorable for the Canadian Beaufort Shelf. We suggest that this enhanced upwelling is forced by the adjustment of the along-shelf flow (that is part of upwelling circulation) to the isobath divergence at the cape. Mooring and drifter data near Cape Bathurst also support this, showing swift, surface-intensified along-isobath flow during upwelling-favorable surface stress. Benthic samples near the cape show high numbers and diversity of organisms which suggest that nutrients brought to the surface by upwelling allow additional primary production in the region that ultimately feeds the benthos

Cooling processes in deep, temperate lakes: A review with examples from two lakes in British Columbia

The cooling period in deep, temperate lakes includes the breakdown of the seasonal thermocline, isothermal overturn as the lake cools through 4°C, and winter restratification. The first part of this paper is taken up with a review of the relatively few studies on the seasonal cooling of lakes...

Thermohaline structure and variability in the eastern Nansen Basin as seen from historical data

Newly available historical Russian data are used to quantify year-to-year variations in the structure and properties of the halocline and Atlantic Water layers in the eastern Nansen Basin. The data come from a series of aerial surveys of the central Arctic Ocean done during winter between 1973 and 1979, and repeated Polygon surveys of the shelf, slope, and basin north of Severnaya Zemlya in the 1980s, and thus allow a perspective on shelf-basin exchange. A water-mass census shows substantial survey-to-survey variability in several water-mass categories, with volumetric fluctuations of ∼17% in the Upper Polar Deep Water category, ∼14% in Atlantic Water, and ∼39% for cold surface waters with T \u3c −1.5°C. Mean water-mass production rates in the polygon area are found to be 0.6–1.2 Sv for Upper Polar Deep Water, and an effective loss rate of 0.75–1.5 Sv is found for Atlantic Waters. On average Atlantic Water loses 16% of its initial heat content within the 350 km-long survey area, possibly enhanced by double-diffusive processes. Mean upward heat fluxes above the Atlantic Water are estimated to be between 4 and 6 W/m2, based on heat budget considerations. Upward heat fluxes of this magnitude would have a major effect on sea ice, which is regularly observed to be thinner in this area of the Nansen Basin. Shallow-water profiles taken close to Severnaya Zemlya show cold and salty waters denser than offshore waters at similar depths, and evidence of convection is seen in many profiles taken over the continental shelf and slope, reflecting deep convective events extending in some cases below the deepest observed depth of 1000 m

Oxygen isotope ratio, barium and salinity in waters around the North American coast from the Pacific to the Atlantic: Implications for freshwater sources to the Arctic throughflow

In 2002, oxygen isotope ratios of water (H218O/H216O), dissolved barium, and salinity were measured in surface waters around northern North America to identify freshwater sources and to provide a large-scale background for interpretation of regional inputs and processes. Oxygen isotope ratios showed that precipitation, river runoff, and sea ice meltwater were all significant contributors to the freshwater carried by the coastal component of the Arctic throughflow. Precipitation and runoff contributed \u3c40% and \u3e60%, respectively, to the freshwater found in surface waters along the Pacific coast. Sea ice meltwater contributed up to 65% to waters residing near the Mackenzie River and in the Canadian Arctic Archipelago. The salinity-barium relationship, after being corrected for dilution by sea ice meltwater, indicated that freshwater from the Mackenzie River flowed eastward into Amundsen Gulf. It did not, however, continue eastward through Dolphin Union Strait and Coronation Gulf in 2002. In the eastern part of the Canadian Arctic Archipelago, Baffin Bay and the Labrador Sea, barium concentrations in surface waters were low, the result of biological activity and/or local freshwater inputs with low barium concentrations

Arctic Ocean Microbial Community Structure before and after the 2007 Record Sea Ice Minimum

Increasing global temperatures are having a profound impact in the Arctic, including the dramatic loss of multiyear sea ice in 2007 that has continued to the present. The majority of life in the Arctic is microbial and the consequences of climate-mediated changes on microbial marine food webs, which are responsible for biogeochemical cycling and support higher trophic levels, are unknown. We examined microbial communities over time by using high-throughput sequencing of microbial DNA collected between 2003 and 2010 from the subsurface chlorophyll maximum (SCM) layer of the Beaufort Sea (Canadian Arctic). We found that overall this layer has freshened and concentrations of nitrate, the limiting nutrient for photosynthetic production in Arctic seas, have decreased. We compared microbial communities from before and after the record September 2007 sea ice minimum and detected significant differences in communities from all three domains of life. In particular, there were significant changes in species composition of Eukarya, with ciliates becoming more common and heterotrophic marine stramenopiles (MASTs) accounting for a smaller proportion of sequences retrieved after 2007. Within the Archaea, Marine Group I Thaumarchaeota, which earlier represented up to 60% of the Archaea sequences in this layer, have declined to <10%. Bacterial communities overall were less diverse after 2007, with a significant decrease of the Bacteroidetes. These significant shifts suggest that the microbial food webs are sensitive to physical oceanographic changes such as those occurring in the Canadian Arctic over the past decade

Deterioration of perennial sea ice in the Beaufort Gyre from 2003 to 2012 and its impact on the oceanic freshwater cycle

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 1271-1305, doi:10.1002/2013JC008999.Time series of ice draft from 2003 to 2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the Beaufort Gyre (BG), culminating in the extreme minimum in 2012. Negative trends in median ice drafts and most ice fractions are observed, while open water and thinnest ice fractions (<0.3 m) have increased, attesting to the ablation or removal of the older sea ice from the BG over the 9 year period. Monthly anomalies indicate a shift occurred toward thinner ice after 2007, in which the thicker ice evident at the northern stations was reduced. Differences in the ice characteristics between all of the stations also diminished, so that the ice cover throughout the region became statistically homogenous. The moored data are used in a relationship with satellite radiometer data to estimate ice volume changes throughout the BG. Summer solid fresh water content decreased drastically in consecutive years from 730 km3 in 2006 to 570 km3 in 2007, and to 240 km3 in 2008. After a short rebound, solid fresh water fell below 220 km3 in 2012. Meanwhile, hydrographic data indicate that liquid fresh water in the BG in summer increased 5410 km3 from 2003 to 2010 and decreased at least 210 km3 by 2012. The reduction of both solid and liquid fresh water components indicates a net export of approximately 320 km3 of fresh water from the region occurred between 2010 and 2012, suggesting that the anticyclonic atmosphere-ocean circulation has weakened.Support for Krishfield, Proshutinsky, and Timmermans, partial financial support of logistics, hydrographic observations on the board of Canadian icebreaker, and full financial coverage of all mooring instrumentation was provided by the National Science Foundation (under grants OPP-0230184, OPP-0424864, ARC-0722694, ARC-0806306, ARC- 0856531, ARC-1107277, and ARC- 1203720), and Woods Hole Oceanographic Institution internal funding. Funding for Tateyama was provided by the International Arctic Research Center – Japan Aerospace Exploration Agency (IJIS) Arctic project, and for Williams, Carmack, and McLaughlin by Fisheries and Oceans Canada