An Eye in the Ocean Exploration of High -Resolution Vertical Distributions of Plankton and Particles and Coincident Hydrography in the Western Chukchi Sea Using a Video Plankton Recorder

Carin Ashjian, Woods Hole Oceanographic Institution

In the Arctic Ocean, the biological response to climate change should be dramatic yet is
difficult to predict because many basic components of the ocean system are undescribed.
Plankton community composition, spatial (vertical, regional) and temporal (diel, seasonal,
annual) patterns in distribution and abundance, and the associations of species and taxa with
water mass type remain enigmatic for much of the Arctic ecosystem. In particular, the
interaction of physical mechanisms with biological distributions is poorly described, especially at
dynamic boundaries. The western Chukchi Sea is strongly influenced by the nutrient-rich Pacific
Water that flows through Bering Strait northwards, exiting the Chukchi Sea primarily through
Herald Valley. Strong regional variation in plankton distribution, abundance, and composition in
association with the distinct water mass types present should be observed. Herald Valley is a
critical region where physical mechanisms impact biological distributions. Such interactions are
best observed using instruments capable of resolving high-resolution distributions of planktonic
taxa and particles and coincident hydrographic and velocity characteristics.
The overall goal of the proposed work is to describe the high-resolution vertical
distributions of zooplankton and particles over a range of spatial and temporal scales. Video
Plankton Recorder Surveys will be conducted in 2012 as part of the RUSALCA interdisciplinary
cruises. Both a broad-scale survey of the different water masses and regions of the Chukchi Sea and a high-resolution survey of Herald Valley will be conducted to obtain the high-resolution distribution of plankton/particles and coincident hydrography and to describe physical-biological interactions in Herald Valley. The VPR data from the three RUSALCA interdisciplinary cruises (2004, 2008, 2012) then will be compared to determine inter-annual variability and to understand if climate change is modifying the ecosystem. Relative backscatter data from two moored acoustic Doppler current profilers that will be deployed at the mouth and to the SW of Herald Valley for a year will be used to describe daily, seasonal, and annual patterns in the vertical distribution and relative abundance of backscatter (zooplankton) and the associations of these characteristics with hydrographic structure and currents.
The proposed work is relevant both to NOAA’s Climate Goal that targets understanding
and predicting climate variability and its impact on ecosystems and to the performance measures of the RUSALCA program. Predicting the impact of climate on ecosystems requires an
understanding of the important components and interactions in the ecosystem, both to identify
change and to develop a predictive modeling capability for the ecosystem. This work will
provide key distributions and processes for this understanding and capability. The work will
characterize the plankton communities of the water masses and regions of the Chukchi Sea
during ongoing climate change, will periodically survey key variables (water masses, plankton)
to identify responses to climate change, and will document how the changing physical