Arctic
Arctic
        Since September of 2006, two HARPs have been twice deployed to the seafloor near the edge of the continental shelf in the vicinity north of Barrow, Alaska. The purpose for this long-term monitoring is to initiate a physical and biological study in the Arctic Ocean using passive acoustics. The physical objective of this project is to establish and characterize baseline measurements for ambient noise levels in the Arctic Ocean, while examining the variability and distinct characteristics that are inherent in seasonality shifts.
  During winter months when the majority of the Arctic Ocean is covered with sea ice, there is minimal noise contributions from environmental variables (e.g. wind and waves) and man-made sources (e.g. shipping and seismic activity). Ambient noise levels are remarkably low across a wide frequency band and can reach levels as much as 20dB below sea state zero. Making calibrated sound pressure level measurements in this type of shallow waveguide may potentially provide the groundwork to later explore changes in acoustic propagation and transmission loss, in most part a direct effect of the alarming decline in sea ice extent, thickness, and overall concentration.
         In contrast to the darkness of winter, the late spring and summer months bring abundant amounts of solar radiation to northern Arctic latitudes, forcing ice to break up and melt as sea surface temperature once again rises. The sun will once again fade in the fall, allowing new ice to build up and form. Both of these transition phases essentially define seasonality trends and are characterized by a plethora of naturally induced noise events. In general, we must consider the variability of noise levels based on temperature, pressure, and wind speed. Arctic noise however is extremely variable on temporal time scales across regions of moving ice masses and marginal ice zones. Ice flow boundary events are described by three forces: rafting, shear ridging, and pressure ridging. Most commonly, we will encounter noise level fluctuations defined by hydrodynamic fluctuations (<1Hz), stress relief (~10Hz), ridge building (<10Hz), shear zone crunching, thermal cracking (100-350Hz), propagating fractures, rubbing and scratching harmonics, ice crystals blowing over surface (2-10kHz), microseisms in Arctic ridge (4-5Hz), wave slap and flow bumping (marginal sea ice zone).
Description of animation.
Ice concentration from March 2007 (Arctic winter) through September 2007
(Arctic summer).

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        The summer of 2007 set a new record low for Arctic sea ice extent, and researchers are concerned that the Arctic may be on the verge of a fundamental transition toward seasonal ice cover. This means a seasonally ice-free Arctic Ocean may be realized as early as 2030 (Stroeve et al, 2007). The acoustic data presently being collected will serve as a comparison as sea ice concentrations rapidly shift during future studies. Before all the multiyear ice disappears, it is imperative to examine the increases in ambient noise levels measured across large temporal scales, and determine the sources of sound that can be attributed to these changes, especially as an effect of different seasonal fluctuations. Long-term acoustic monitoring is our best hope in understanding these changes, as year-long datasets exploit the seasonal variability of sea ice in a specific location. Other possible contributors to these increases are seismic activity, oil and gas extraction, and commercial shipping.

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          The biological objective of this study is to monitor Arctic marine mammals migrating or foraging in the near-shore and coastal regions of Barrow, Alaska. This project was initially funded by Robert Small of the Alaska Department of Fish and Game. Vocalizations identified in the data include Bowheads, Belugas, Ringed seals, Bearded seals, and Walrus. Major concern arises when considering how a seasonally ice-free Arctic will affect the behavior of mammals that have adapted to such harsh conditions over time, and how the introduction of invasive biological mechanisms will alter ecosystem dynamics. Cetaceans on the move are dependent on the state of the seasonal ice pack, especially as leads (i.e. passageways) open and close during ice transition periods. Pinnipeds need the ice to haul out on during foraging periods. Many of these mammals are bottom feeders and require relatively shallow environments in order to dive deep enough to find sufficient sources of food. As the ice edge is constantly shifting north, these mammals are losing their hunting grounds and being forced into desperate acts for survival. This includes polar bears as well, being that their main source of prey are ice seals. Aside from the survival of these marine mammals, we must consider the impact that all this will have on Inupiaq subsistence hunting.
         While the general intent of this study is to compare data measurements collected from future instrument deployments, there is already a wealth of transient events to be analyzed and subsequently characterized in the context of the Arctic environment at present. Our acoustic data is correlated with ancillary data such as satellite measurements of sea ice extent and concentration, in addition to meteorological data recorded by weather stations in Barrow.
Arctic Low - September 1987
Arctic Low - September 1997
Arctic Low - September 2007
     

Subsequent data will be evaluated against the same time period, providing forscientific objectivity and unbiased sampling due to the time-variant change in sea ice declination, essentially an effect linked to climate change. The unprecedented warming occurring in Arctic latitudes is the primary mechanism for this driving force, yet climate models have been unsuccessful in accurately predicting the future of sea ice due to many unknown parameters such as predicting the albedo feedback mechanism, ice thickness variability, and unusual patterns of atmospheric circulation (Maslanik et al, 2007).
         In 2003, SIO initiated a bowhead acoustic monitoring project off the north slope of Alaska with support from NOAA National Marine Mammal Laboratory/Alaska Fisheries Science Center. ARPs were deployed from the USCGC Healy in collaboration with Woods Hole and the NSF-funded Shelf-Basin Interaction program (SBI). The purpose of the initial deployments was primarily to monitor bowhead whale calling during the fall and spring migration. We conducted subsequent deployments in 2006 and 2007, with the most recent sites slightly north and west of Point Barrow. ARPs in 2006 and 2007 sampled at higher frequencies, allowing us to detect a wider variety of sounds including beluga whales, pinnipeds, ice, and manmade noises. These acoustic data are being recorded at a crucial point in time as the Arctic ecosystem shifts to a warmer, more ice-free state, with the potential for increased shipping and human activity as well as biological responses to change.

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Credit: Ethan Roth