Chief Scientist Synopsis- Cruise NBP04-08
Week 4: November 17 – 23.
Week four of NBP04-05 finally provided the first opportunity to conduct our
standard station operations. While an open water polynya continued to elude us, in situ
fluorescence monitoring indicated that we were entering phytoplankton bloom conditions
as we traveled through areas dominated by new ice. This new station allowed the
Jeffrey/Neale groups (B200/B203) to begin to monitor phytoplankton and
bacterioplankton response to UV in a fully Phaeocystis dominated community. Biomass
varied between low and moderate at the beginning of the station, but increased
dramatically towards the end of the station. Our approach is built around a six day
sampling cycle with two days focused on determination of Biological Weighting
Functions (BWF) for phytoplankton photosynthesis and bacterioplankton growth.
Another two days target experiments to quantify growth inhibition by solar UVR and
subsequent repair and recovery. Additional primary experiments include deployment of
an array to monitor in situ effects of solar irradiance on phytoplankton photosynthesis
and bacterioplankton growth. In this case, the array was quickly engulfed in pancake ice
during the majority of its deployment. Nevertheless, we observed light effects to 4
meters below the surface. Our final experiment is a diel/depth profile experiment where
we monitor solar UV effects over a 24 hr period in surface and waters down to 20 meters.
Critical parameters are production and DNA damage and it is this experiment, in
conjunction with the Gargett project (B208), where we most closely combine biological
effects with measures of water column mixing. Preliminary results on phytoplankton
quantum yield suggest a simultaneous build up of phytoplankton biomass and transition
of the phytoplankton community from an iron sufficient to iron limited status. A
preliminary experiment indicated that bacterioplankton were also iron limited as well as
carbon limited for growth. The opportunity to measure UV responses during this
transition motivated the extension of the station period to a seventh day.
OPP post doctoral Fellow Brook Nunn (B200) continued depth profile sample
collection for trace metal analysis, organic carbon (DOC and TOC), nutrients, particulate
trace metal fractions and dissolved proteins. Additional samples were collected via
zodiac to monitor trace metals in sea ice slush and melt waters. Ice slush with visibly
high algae concentrations were sampled to analyze the size fractionation of particulate
iron (and other metals) and differential protein expression in the ice algae. Biomass was
concentrated via plankton net tows for trace metal analyses and protein expression.
The Gargett team (B208) continued to run yo-yo CTD casts for overturning scale
analysis several times a day. In the mainly ice-covered environment of operations during
this week, most profiles contained only small (<1m) overturns. However one yo-yo
session sampled a 40m overturn across the mixed layer base. This feature was present
only on a single up-cast and the succeeding down-cast, suggesting a surprisingly small
spatial scale for such massive overturns. We continued to work on the HTI two-frequency
towed backscatter sonar system. The high frequency (120KHz) transducer is definitely
inoperable, and shallow operating depths in the study area produce multiple bottom
echoes in the 38KHz return that can obscure the desired near-surface measurement range.
In addition, trying to measure small signatures of ocean processes in the presence of shipgenerated turbulence has been a major challenge. However working with the crew and
officers of the NBP, we discovered a successful deployment technique that allowed
uncontaminated measurements of the backscatter features associated with Langmuir
circulations. Distinctive backscatter clouds (of either air micro- bubbles and/or grease ice
particles) occur under the “ice lines” that form on the surface of even small (< 1 mile)
open water areas in windy conditions. We interpret these lines of grease ice as the
manifestations of surface convergences associated with the downwelling limbs of
Langmuir cells. With 20 Kt winds, the associated backscatter clouds extend to a
minimum depth of 10m, revealing the minimum extent of active mixing driven directly
by this surface wind/wave process.
The Gast/Caron group (B-207) continued to collect and process water samples,
examining surface water and depth profiles for changes in microbial community
composition during the time that we were on station. Ice samples were collected on the
second to last day of the station from potentially multi-year floes trapped in younger ice.
Six cores total were taken, 4 for nucleic acid based analysis and two for
mixotroph/bacterivory experiments. These experiments have continued for water and ice
samples, and indicate that mixotrophy is consistently present even this relatively early
stage of the phytoplankton bloom. Single cell isolations and DNA-based analyses are
working well, particularly on net tow samples and slush/ice samples
The Goes group (B206) began a new long term experiment to examine the
combined effects of UVR and iron enrichment on phytoplankton growth rates, production
of fatty acids, amino acids, carbohydrates and MAAs of phytoplankton communities
associated with sea ice melt. An additional goal of this experiment is to examine whether
iron enrichment could lead to significant differences in the composition of phytoplankton
community structure in the presence and absence of UVR. Experiments were also
conducted with plankton net collected samples to examine the wavelength dependency of
carbon incorporation into fatty acids, amino acids and carbohydrates. Samples for these
experiments were collected by means of a plankton net. A final experiment was initiated
to examine the effects of salinity changes on the growth of phytoplankton communities
associated with slush ice.
The Kiene/Kieber group (B002/B266) conducted several seawater incubations to
assess the day-long effects of UV-B, UV-A, and visible light on: 1) the biological
consumption of DMS and DMSP, 2) the biological production of DMS, and 3) the
photochemical loss of DMS. A long-term sulfur transformation experiment (8 day
incubation) was also initiated exposing 2 L aliquots of 20 m seawater to sunlight with and
without UV. Ultraviolet light doses in the incubators were monitored by chemical
actinometry. Polychromatic irradiations were also conducted to resolve the wavelength
dependence for DMS photolysis and consumption, and the biological loss of DMSP and
production of DMS. CTD casts were deployed to determine concentrations of DMS,
dissolved and particulate DMSP and DMSO were determined as a function of depth in
the water column. Ancillary measurements included CDOM absorbance, nutrients,
chlorophyll, pigments, and PAM fluorometry to quantify Fv/Fm. Two over-the-side
deployments were made with the Biospherical PRR to characterize the downwelling and
upwelling irradiance of the six visible SEAWIFS channels in the upper 30 m of the water
column. Finally, several plankton, krill and particulate samples were collected for carbon
and nitrogen stable isotope analysis.
This week finally provided an opportunity for all projects to proceed full ahead.
Several technical and methodological hurdles were overcome in time to work in the
Pheaocystis dominated waters expected during this time of year in the Ross Sea. Our
work was greatly facilitated by the excellent assistance of both RPSC and ECO staff and
crew. We are particularly impressed with their tireless efforts during the 24 hr diel
experiments and we thank them for their efforts.
Respectfully Submitted,
Wade H. Jeffrey and Patrick Neale