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Frontal Structures in the West Spitsbergen Current Margins

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EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Open Access Open Access Climate Climate of the Past of the Past Discussions Open Access Open Access Earth System Earth System Dynamics Dynamics Discussions Open Access Geoscientific Geoscientific Open Access Instrumentation Instrumentation Methods and Methods and Data Systems Data Systems Discussions Open Access Open Access Geoscientific Geoscientific Model Development Model Development Discussions Open Access Open Access Hydrology and Hydrology and Earth System Earth System Sciences Sciences Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Open Access Ocean Sci. Discuss., 10, 985–1030, 2013 Open Access www.ocean-sci-discuss.net/10/985/2013/ Ocean Science OSD doi:10.5194/osd-10-985-2013 Ocean Science Discussions © Author(s) 2013. CC Attribution 3.0 License. 10, 985–1030, 2013 Open Access This discussion paper is/has been under reviewOpen Access for the journal Ocean Science (OS). Frontal structures in Please refer to the corresponding final paper in OS if available. Solid Earth Solid Earth Discussions the West Spitsbergen Current margins Open Access Open Access W. Walczowski The Cryosphere The Cryosphere Frontal structures in the West Discussions Spitsbergen Current margins Title Page Abstract Introduction W. Walczowski Conclusions References Institute of Oceanology Polish Academy of Sciences, Powstancow Warszawy 55 81-712 Sopot, Poland Tables Figures Received: 14 May 2013 – Accepted: 14 June 2013 – Published: 2 July 2013 J I Correspondence to: W. Walczowski ([email protected]) J I Published by Copernicus Publications on behalf of the European Geosciences Union. Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 985 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract OSD The structures of the hydrographic fronts separating the Atlantic origin waters from am- bient waters in the northern Nordic Seas are discussed. Flows of the western and east- 10, 985–1030, 2013 ern branches of the West Spitsbergen Current create the Atlantic domain borders and 5 maintain these fronts. The work is based on previous research and on investigations in Frontal structures in the project DAMOCLES (Developing Arctic Modeling and Observational Capabilities for the West Spitsbergen Long-term Environmental Studies). Most of the observational data were collected dur- Current margins ing the R/V Oceania cruises. The main focus of the paper is put on the western border of the Atlantic domain – the Arctic Front, along- and transfrontal transports, the front W. Walczowski 10 instability and variability. The baroclinic instability and advection of baroclinic eddies which occurs due to this instability were found as the main transfrontal transport pro- cesses. Most of the Atlantic Water transported by the western branch recirculates west Title Page and southward. The eastern branch of the West Spitsbergen Current provides most of Abstract Introduction the Atlantic Water entering the Arctic Ocean. Both processes are very important for the 15 Arctic and global Thermohaline Circulation. Conclusions References Tables Figures 1 Introduction J I Most of the Atlantic Water (AW) that enters the Nordic Seas (Norwegian, Greenland, and Iceland Sea) flows over the Faroe-Iceland Ridge and between the Faroe and Shet- J I land Islands (Hansen and Osterhus, 2000). There are two main branches of the AW Back Close 20 inflow east of Iceland. The colder, less saline western branch (the Faroe Branch) of the Norwegian Atlantic Current is topographically guided from the Iceland-Faroe Front Full Screen / Esc towards the Fram Strait (Fig. 1). In the Nordic Seas it acts as the jet of the Polar Front (Orvik and Niiler, 2002). The warmer, more saline eastern branch of the AW (the Shet- Printer-friendly Version land Branch) enters the Nordic Seas through the Faroe-Shetland Channel and con- Interactive Discussion 25 tinues north along the Norwegian shelf edge as the Norwegian Atlantic Slope Current (NASC) (Orvik and Skagseth, 2003). After passing the northern Norway, the NASC 986 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | branches. One stream of the AW enters the Barents Sea as the North Cape Current (the Barents Sea Branch) and flows into the Arctic Ocean (AO), mostly through the St. OSD Anna Trough (Schauer et al., 2002; Maslowski et al., 2004). The second branch contin- 10, 985–1030, 2013 uing north along the continental slope is called the West Spitsbergen Current (WSC) 5 (Aagaard and Carmack, 1989). Nowadays this flow is often called the WSC eastern branch or the core of the WSC; correspondingly, the continuation of the Faroe Branch Frontal structures in linked with the oceanic frontal system is called the WSC western branch. These two the West Spitsbergen currents and hydrological fronts related to the both branches of the WSC create dy- Current margins namic borders of the region occupied by the AW – the Atlantic domain (AD) of the W. Walczowski 10 Nordic Seas (Fig. 1). There is a large scale oceanic front in the west, and shallow wa- ter, local scale front in the east. Both fronts separate the Atlantic-origin waters from the ambient, much colder and fresher water masses. Title Page In the Nordic Seas the Meridional Overturning Circulation (MOC) becomes more of a horizontal loop. The warm, buoyant waters flow northward in the east, the cold, Abstract Introduction 15 dense waters flow towards the Atlantic in the west (Mauritzen, 2011). This two way oceanic exchange that connects the Arctic and Atlantic oceans are of fundamental Conclusions References importance to climate (Dickson et al., 2008). The importance of the fronts – flexible Tables Figures borders between warm and cold water masses is related to the importance of the whole Nordic Seas for the global climate. J I 20 Fronts create the barrier between waters of different properties and origin. There are strong horizontal gradients of all properties across the front. Contact of water masses of J I various densities generates alongfrontal baroclinic jet streams, which keeps the front Back Close in the dynamic equilibrium state (Fedorov, 1986). This frontal barrier is not solid – frontal zone changes its position, water mixes and exchanges across the front. In the Full Screen / Esc 25 case of the Atlantic domain in the Greenland Sea, processes of transfrontal exchange, especially through the western border are very important; it is the vital part of the Printer-friendly Version northern limb of the Atlantic Meridional Overturning Circulation (AMOC). Water masses formed in the Nordic Seas and the Arctic Ocean supply the Greenland-Scotland Ridge Interactive Discussion 987 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | overflow and maintain the lower limb of the Atlantic Meridional Overturning Circulation (Kuhlbrodt et al., 2007). OSD Existence of the intensive northward current over the Mohn and Knipovich Ridges 10, 985–1030, 2013 has been postulated for a long time (Dietrich et al., 1980). Old maps of Alekseev and 5 Isothin from 1955 showed 3 branches of the Norwegian Atlantic Current, in Wegner’s map from 1963 splits of the North Atlantic Current into 2 branches of the Norwegian Frontal structures in Current at the latitude of southern Norway occurs. Both branches re-join west of Sval- the West Spitsbergen bard (Fig. 2). Also, the Institute of Oceanology, Polish Academy of Sciences (IOPAN) Current margins works (Piechura and Walczowski, 1995; Walczowski, 1997) suggested existence of the W. Walczowski 10 second WSC branch formed by the baroclinic alongfrontal jet streams. For a long time the role of these flows was not appreciated. The common mistake made by all authors was claiming that both NAC branches originate from only one Title Page AW inflow through the Faroe-Shetland Channel. Monitoring the Faroe Branch (Hansen et al., 1999) of Atlantic inflow over the Greenland-Scotland Ridge in late 90s helped Abstract Introduction 15 understand the AW pathways in the Nordic Seas. In this work the frontal structures bordering the northern part of the AD and several Conclusions References processes occurring there are described. The additional aim of this study is to quantify Tables Figures the importance of the hydrographic fronts separating the Atlantic Waters in the Nordic Seas from other water masses. The used data sets and applied methods are intro- J I 20 duced in Sect. 2. In Sect. 3, the structure of the AD is described. Section 4 provides a description of the western AD border, and Sect. 5 refers to the eastern AD border. J I Section 6 summarizes the main conclusions of the present study. Back Close Full Screen / Esc 2 Data and methods Every summer since 1987, the IOPAN research vessel Oceania operates in the region Printer-friendly Version 25 between the northern Norway and the Fram Strait. The main objectives of this work Interactive Discussion include investigation of the AW flow through the Norwegian and Greenland Seas, water properties and modification.
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