Chief Scientist Synopsis - Cruise NBP05-08
Week 3: November 10 - November 16, 2005
This was our first full week of operations in the Ross Sea Polynya region. After a
one day occupation of a low biomass station near the Ross Ice Shelf, we moved
northward approximately 70 miles to a site just east of Franklin Island where
phytoplankton are growing in a surface layer below a thin cover of new and young ice.
This site was chosen for a multiple day station focusing on the responses of a pre-polynya
community. During this station open water remained scarce, but in situ fluorescence
suggested that phytoplankton biomass was increasing. We were able to conduct most
planned laboratory and deck incubations but conditions were unsuited to in situ
deployments. Nevertheless, we remained in the area until we received needed supplies
that were brought to us via helicopter from McMurdo. The travel to the helicopter
rendezvous site and waiting for the delivery occured on the last two operating days of the
week. Microscopic examination indicated that the phytoplankton community in this area
was dominated by diatoms, so after delivery we headed eastward to where satellite
imagery suggests more open water and higher biomass of Phaeocystis which is the
priority for several of our planned experiments.
During this multiple day station, the Neale/Jeffrey groups (B203/200) conducted
incubations for UV biological weighting functions for both phytoplankton primary
production and bacterioplankton heterotrophic production. Deck incubations were
performed to track the time scales of inhibition and recovery of these processes under
solar ultraviolet exposure. Regular profiles were conducted with the in situ Fast
Repetition Rate Fluorometer (FRRF). These alternate with CTD drops by the Gargett
group (B208) to monitor water column vertical motion (Thorpe overturning scales). The
Gargett group continued efforts to use towed acoustic sonar to infer near surface mixing
processes. The Jeffrey group also conducted the first diel experiment using 2 hr sampling
intervals for 24 h to examine patterns of DNA damage and bacterial production. They
also conducted daily experiments to examine UVB induced DNA damage in the
planktonic assemblage by using size fraction filtration to separate major trophic groups.
OPP Post Doctoral Fellow Brook Nunn began collecting water samples using trace metal
clean techniques and subsequent isolation of cellular proteins. The primary activities of
the Kieber/ Kiene group (B266/002) were to determine water column concentrations of
dimethyl sulfide (DMS), dimethyl sulfoniopropionate (DMSP) and dimethyl sulfoxide
(DMSO), and conduct a series of experiments, employing radiolabeled 35S-DMS and DMSP, to assess the effects of UV and visible light on the rates of biological production
and loss of these compounds in seawater collected from the surface mixed layer. They
also conducted polychromatic incubations to assess the wavelength dependence for
different sulfur transformations. Deep CTD casts were deployed to determine sulfur
concentrations seawater well below the photic zone to assess deep water inputs of organic
sulfur, presumably derived from abiotic and biological processes in the photic zone.The
Goes group (B206) started deck incubation experiments to study the effects of UV
radiation on rates of carbon incorporation into fatty acids, carbohydrates and amino acids
in phytoplankton communities drawn from different depths within the water column.
These experiments were repeated over the first three days of the station. In addition,
seawater samples collected by means of a Zodiac at a distance away from the ship were
utilized to commence our experiments for investigating the combined effects of UV
radiation and iron enrichment on the uptake rates of nitrate, ammonia, urea and carbon
over short and prolonged exposure periods. Another major operation on Day 3 of the
station was deployment of a drifting sediment trap and in-situ incubation array. The array
was beset with heavy ice as weather deteriorated, so the planned 24 h mooring was
recovered approximately 7 hrs after deployment. The Gast/Caron group (B207) is
continuing experiments to survey changes in grazing on bacteria and mixotrophy due to
spatial (and temporal) changes. Analyses include DNA based community structure and
microscopic assessment of bacterivory and the proportion of autotrophs that are also
mixotrophic. Water samples were also been collected on the first and last day of the
station to examine protistan community structure at early stages of the spring bloom.
Both DNA and RNA are being analyzed to determine the difference between the cells
present and the cells that are active. In addition to water, several sets of ice samples were
taken during this week to compare with the water column communities. Cores were
shared with the Jeffrey group for bacterial analysis. One set came at the end of the
occupied station, with the cores showing a slight bottom community and an internal
channel. The other two sets were collected from the fast ice and showed a strong bottom
community with internal channels. The bottom community was dominated by diatoms
(as expected), but the internal channel was almost exclusively dinoflagellates.
Construction of clone libraries continues to progress with about half of the samples
archived for sequencing. Quantitative PCR analyses for the kleptoplastidic dinoflagellate
of interest also continues to work well.
Overall, scientific operations have been going well considering the early spring
conditions. Several days of more benign weather this week aided in alleviating problems
with maintaining flowing water incubators. Another critical factor in success has been
good coordination in operations between RPSC, ECO and science groups. Special
recognition this week goes to NBP and MCM based personnel for logistic support in the
rapid turn-around helicopter delivery of supplies upon arrival of air shipment in MCM.