ジュネーブ湖の自然流氷を科学者が解明(Scientists delve into natural slicks on Lake Geneva)


EPFLの研究者は、スリック(滑らかな水の塊)が動く様子を初めて記録し、水面下で何が起きているのかを説明しました。 An EPFL researcher has, for the first time, documented slicks – those visually arresting, moving patches of smooth water – and explained what is happening beneath the surface.

2023-01-11 スイス連邦工科大学ローザンヌ校(EPFL)

 スイス人画家のフェルディナンド・ホドラーは、湖の滑らかな表面とその特徴的な質感に光が反射する様子を巧みに捉えています。EPFLの建築・土木・環境工学部(ENAC)の生態工学研究所(ECOL)の所長であるアンドリュー・バリーと、ECOLの博士課程に在籍するMehrshad Foroughanは、神秘的で興味をそそられる現象である、ジュネーブ湖の天然のスリックについてもっと知りたいと思い、このテーマを卒論にすることにしました。彼の研究成果の一部は最近『Geophysical Research Letters』に掲載され、湖の流体力学についてスリックから何がわかるかについて初めて文書化された研究である。



サブメソスケールでの持続的な前線スリック。大規模湖(ジュネーブ湖)におけるメソスケール流れ場の新しいマーカー A Persistent Submesoscale Frontal Slick: A Novel Marker of the Mesoscale Flow Field in a Large Lake (Lake Geneva)

Mehrshad Foroughan, Seyed Mahmood Hamze-Ziabari, Ulrich Lemmin, David Andrew Barry
Geophysical Research Letters  Published: 21 October 2022


Submesoscale fronts often become visible when the accumulation of biosurfactants in the water surface microlayer causes smooth surfaces, called frontal slicks, to develop. Based on in situ and remotely-sensed data, a frontal slick was documented for the first time in a lake (Lake Geneva). A quasi-stationary ∼10-km long slick formed on the warm side of a surface temperature front with strong horizontal velocity strain. The slick width increased from ∼50 to ∼200 m in ∼1.5 hr due to “feeding” by wind-driven, rapidly-moving smaller slicks. Numerical modeling results, confirmed by satellite data, indicated that the boundary between mesoscale gyres isolated warm surface water from cold water associated with wind-induced coastal upwelling. Measurements and modeling suggest that frontogenetic sharpening of the submesoscale temperature gradient created an active front with strong convergent flow. Such dynamics must be considered in buoyant material transport and the vertical exchange of surface water with deeper layers in lakes.

Key Points

  • A submesoscale frontal slick is documented in a lake for the first time; it evolved on the warm side of a surface temperature front
  • The temperature front was formed by mesoscale circulation that separated relatively warm surface water from colder upwelling-induced water
  • The slick was 10-km long and its width increased by a factor of four in 1.5 hr due to “feeding” by wind-driven small-scale slicks

Plain Language Summary

Near-surface currents in lakes are affected by interactions of structures of different scales, such as gyres, eddies and coastal upwelling. These interactions can lead to the formation of fronts that are zones of convergence and downwelling, leaving floating materials to concentrate on the surface. Fronts are important because they can modify the lateral transport of surface material and the exchange between near-surface and deeper layers. Among the floating materials, biosurfactants create smooth surface areas (slicks) by suppressing capillary gravity waves, thus allowing visual detection of fronts in remote imaging. This study, carried out in Lake Geneva, documents for the first time the existence of a submesoscale (∼10 km) frontal slick in a lake. Three-dimensional numerical modeling and satellite imagery showed that due to the interaction of mesoscale gyres and eddies with coastal upwelling, a thermal front was generated in the area where the frontal slick was observed. In situ field measurements provided evidence that the observed slick was located on the warm side of the predicted thermal front. Since frontal slicks are easy to observe and track, they can provide valuable information about mesoscale dynamics in lakes, which at present are poorly understood.