The surface temperature structure associated with the Keweenaw Current in Lake Superior

Green, T.; Terrell, Robert E.

doi:10.1029/jc083ic01p00419

Cited by 15 publications

(4 citation statements)

References 20 publications

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“…A primary focus of KITES is a seasonal coastal flow known as the Keweenaw Current. Flowing northeastward along the western shoreline of Lake Superior's Keweenaw Peninsula (Figure 1), this current tends to intensify downstream and can reach speeds on the order of 1 m s −1 near the tip of the peninsula [ Yeske and Green , 1975; Niebauer et al , 1977; Green and Terrell , 1978; H. J. Niebauer and E. A. Ralph, Episodic events in the Keweenaw Current in Lake Superior: A retrospective, submitted to Journal of Geophysical Research , 2004, hereinafter referred to as Niebauer and Ralph, submitted manuscript, 2004]. A numerical modeling investigation by Chen et al [2001] and Zhu et al [2001] has indicated that the Keweenaw Current is partly a thermally driven flow, caused by rapid warming of nearshore (versus offshore) water.…”

Section: Settingmentioning

confidence: 99%

Bottom stress generation and sediment transport over the shelf and slope off of Lake Superior's Keweenaw peninsula

2004

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[1] Data from near-bottom instruments reveal that the mechanisms responsible for generating bottom stresses and resuspending sediment over the shelf and slope off of Lake Superior's Keweenaw peninsula exhibit distinct seasonal variations. Notably, near-bottom flows over the slope are persistently weak (<10 cm s À1 ) during summer but frequently attain high speeds, in excess of 20 cm s À1 , in autumn and winter. During the intense storms of autumn and winter the generation of bottom stress is enhanced by the action of near-bottom orbital velocities due to surface waves. Even at 90-m depth, orbital velocities can increase bottom stress by a factor of up to 20% during storms. Where the seasonal thermocline intersects the lake floor, bottom stress is also considerably enhanced, often by more than a factor of 2, by high-frequency motions in the internal wave band. Over the Keweenaw slope, sediment resuspension is largely confined to autumn and winter episodes of high bottom stress. Our analysis indicates that this resuspended material tends to be carried offshore, a phenomenon that is partly due to the coincidence of the direction of the buoyancy-driven component of the Keweenaw Current with downwelling favorable alongshore winds. As a result of this coincidence, currents and bottom stresses tend to be greater during periods of downwelling, as opposed to upwelling, circulation. A potential challenge to modeling storm-driven resuspension in the study region is indicated by observations that the minimum stress required for resuspension may vary significantly with time over the autumn and winter.

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Section: Settingmentioning

confidence: 99%

Bottom stress generation and sediment transport over the shelf and slope off of Lake Superior's Keweenaw peninsula

2004

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“…Surface water circulation patterns in Lake Superior are dominated by a counter-clockwise, wind-driven current system (Adams, 1970;Smith & Ragotzkie, 1970;Sloss & Saylor, 1976). The surface currents are strongest on the north side of the Keweenaw Peninsula where the Keweenaw Current achieves speeds of up to 90cms-' (Ragotzkie, 1966;Green & Terrell, 1980). The current is well defined and narrow, extending as far as 20 km offshore and confined to the upper 30 m of the water column during the summer when it is best developed.…”

Section: Introductionmentioning

confidence: 99%

Side‐scan targets in Lake Superior—evidence for bedforms and sediment transport

Flood

Johnson

1984

Sedimentology

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A high‐resolution side‐scan sonar survey of the lake bed off the Keweenaw Peninsula, Lake Superior, demonstrates that bottom currents are affecting lake bed morphology at depths up to 240 m. Numerous lineations which run parallel to the shore appear to be sand ribbons. A field of sedimentary furrows which occurs in one area demonstrates the long‐term directional stability of the near‐bottom flow. Large (100–300 m in diameter, 2–5 m deep), unusual ring‐like or arcuate depressions are common throughout the western half of Lake Superior. These rings themselves do not appear to have been formed by bottom currents, but may have developed as water was released by the rapid compaction of glacial sediments which underlie the lake bed. Off the Keweenaw Peninsula the forms of the rings have been modified by bottom currents. The bottom currents which have modified the lake bed are probably generated when storms cross the lake at times when it is poorly stratified.

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“…Likewise, inshore areas contained a concentration of older larvae that unlikely would have formed and persisted if larvae were only passive drifters. They seemed to be able to remain in the study region for a longer duration when at inshore locations or at Ontonagon, where they likely avoided most of the influence of the Keweenaw Current, compared with larvae at farther distances from shore or farther along the Keweenaw coast where waters deepen and the current intensifies (Niebauer et al 1977;Green and Terrell 1978). In fact, larvae at Houghton on 5-7 June were rarely encountered, despite extensive sampling from both north and south transects from distances of 0.5-7.0 km from shore, and during the last cruise, Houghton samples were completely devoid of cisco.…”

Section: Discussionmentioning

confidence: 98%

Transport and growth of larval cisco (Coregonus artedi) in the Keweenaw Current region of Lake Superior

Oyadomari

Auer

2008

Can. J. Fish. Aquat. Sci.

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Larval cisco (Coregonus artedi) were sampled from Lake Superior off the western coast of the Keweenaw Peninsula (Michigan, USA) to determine if the Keweenaw Current influences their distribution and growth. Bongo net tows were conducted during April-June 2000 from four transects extending from 0.1 to 17 km offshore. For most sampling dates, cisco tended to be slightly more abundant, larger, and older at inshore locations. Later-hatched larvae appeared at the western-most transects first, during which time earlier-hatched larvae disappeared from the study area. This pattern followed what would be expected if larvae were being transported eastward by the prevailing Keweenaw Current. Estimated growth rates were 84% higher for later-hatched compared with earlier-hatched larvae and 25% lower for offshore larvae from the eastern-most transects compared with elsewhere. Accordingly, surface water temperatures partly explained spatial and temporal variations in growth rate. These results indicate that cisco larvae in Lake Superior may be transported great distances from major spawning sites by longshore currents and that the temperature regime of nursery areas may largely control their growth.Résumé : Nous avons échantillonné des larves de ciscos de lac (Coregonus artedi) du lac Supérieur au large de la côte occidentale de la péninsule de Keweenaw (Michigan, É .-U.) afin de déterminer si le courant de Keweenaw affecte leur répartition et leur croissance. Nous avons effectué des traits de filets bongo en avril-juin 2000 sur quatre transects allant de 0,1 à 17 km de la rive. Pour la plupart des dates d'échantillonnage, les ciscos avaient tendance à être légèrement plus abondants, plus grands et plus vieux dans les sites près de la rive. Les larves à éclosion plus tardive apparaissent d'abord dans le transect situé le plus à l'ouest, au moment où les larves à éclosion plus hâtive ont disparu de la zone d'étude. Ce patron s'accorde avec ce qu'on peut attendre si les larves sont transportées vers l'est par le courant prédominant de Keweenaw. Les taux de croissance estimés chez les larves à éclosion tardive sont 84 % plus élevés que ceux des larves à éclosion hâtive et ils sont de 25 % inférieurs chez les larves du large dans le transect le plus à l'est par comparaison à tous les autres sites. En conséquence, les températures des eaux superficielles expliquent en partie les variations spatiales et temporelles des taux de croissance. Nos résultats indiquent que les larves de ciscos du lac Supérieur peuvent être transportées sur de longues distances à partir des principaux sites de fraye par les courants côtiers et que les régimes thermiques des zones de nourricerie peuvent en grande mesure contrôler leur croissance.[Traduit par la Rédaction]

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The surface temperature structure associated with the Keweenaw Current in Lake Superior

Cited by 15 publications

References 20 publications

Bottom stress generation and sediment transport over the shelf and slope off of Lake Superior's Keweenaw peninsula

Bottom stress generation and sediment transport over the shelf and slope off of Lake Superior's Keweenaw peninsula

Side‐scan targets in Lake Superior—evidence for bedforms and sediment transport

Transport and growth of larval cisco (Coregonus artedi) in the Keweenaw Current region of Lake Superior

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