14 June 2002 Service Group Science Report Healy – 02 - 01 Brief description of the data suite: During this cruise (HLY - 02 –01), the service team has taken 135 CTD/Rosette Casts to depths as great as 3,000 m at 39 stations. "Raw" CTD plots were made immediately after each cast to guide sampling during subsequent casts. Edited data were mounted on the JOSS web site within ~ 24 hrs. Our observations included CTD-temperature, CTD-salinity, CTD-dissolved oxygen, light transmission, fluorometric chlorophyll, fluorometric dissolved organic matter (Haardt, fluorometer), and PAR (Photosynthetically Active Radiation) determinations. Bottle samples were analyzed for salinity, dissolved oxygen, ammonium, nitrate, nitrite, phosphate, dissolved silicon, urea and chlorophyll. All CTD, temperature, pressure, conductivity, salinity and light transmission data are calibrated and have been edited, They are unlikely to change before the data are submitted as “final”. The same is true for bottle salinity, bottle dissolved oxygen and nutrient data. All other data should be considered to be “preliminary”. Plots of our data in the form of vertical profiles, TS plots, histograms and sections have been completed and been made available to participants. We also performed nutrient analyses for samples collected from the ice, and for various incubation samples. These data were edited and provided to the PI’s who supplied the samples. A complete description of our methods is provided in the companion Service Team Cruise Report. Preliminary Data Analysis: 1. The general Temperature and Salinity structure is more or less as expected. Interesting features include, temperature fine-structure in the halocline and near the core of the Atlantic Water, these arise, in part at least, from the small effect that temperature has on density at the prevailing low temperatures., Surface salinities of less than 30 have been recorded as we moved eastward and offshore into the Beaufort Sea, presumably due to a general freshening of the surface waters as we depart the region under the direct influence of the Bering Strait inflow, and to the accumulated effects of ice-melt and river runoff. At station 10, water with temperatures above 0 was encountered at a depth of ~35 m in a shallow temperature maximum. Shallow temperature maxima were also encountered at stations 8 and 9 but do not appear to be so well- developed. This bolus of water with temperatures > -0.5C dissappeared on our next section (stations 12-22), but there was a relatively warm intrusion with somewhat colder temperatures present at the same approximate depths at several additional stations including some of the stations taken in Barrow Canyon towards the end of the cruise. It may also be worth noting that the T and Salinity vs depth profiles in Barrow Canyon seemed to vary more from station to station than they did in the sections outside of the Canyon. 2. The generalities of the nutrient regime also are more or less as expected with high initial nutrient concentrations over the shelf near Bering Strait decreasing as we proceeded eastward and seaward. Initially, nitrate concentrations at the sea-surface exceeded 15 micromolar, phosphate exceeded 1.8 micromolar and surface silicate concentrations exceeded 40 micromolar, but surface nitrate concentrations became vanishingly small by the time we reached deep water. Phosphate and silicate were always present in appreciable concentrations, but nitrate was sometimes depleted. Although there was some variability, there was a strong onshore-offshore nitrate gradient in our first two sections (stations, 5-11 and 13-22). Nitrate was relatively abundant near shore with maximum surface concentrations > 7 micromolar at the innermost station on the first section (Sta. 5) decreasing to essentially 0 at the outermost station (Sta. 11). At our next station, further to the east, nitrate concentrations at the surface at the innermost station (Sta. 22) were ~ 5 micromolar, decreasing to about 0.2 micromolar at the outermost station (12), and a similar nitrate distribution appeared to prevail on our last section in Barrow Canyon. We did, however, encounter conditions that suggested the initiation of an inshore phytoplankton bloom on our last section. While we expected a strong decrease in nutrients as we departed the region under the direct influence of the Bering Strait inflow, the lack of nitrate in surface waters at the offshore stations was somewhat surprising since we arrived early in the "growing" season. Examination of the nitrate, dissolved oxygen, and chlorophyll data suggest an initial surface nitrate concentration of ~ 3 micromolar which has essentially been consumed by the time of our cruise. In other words, the spring bloom in this nutrient poor region may have already occurred, at least in the surface layer. Observations and comments on productivity in this region are scarce, but we will do our best to ascertain whether this early blooming is "normal" or related to the recent warming of the Arctic. Certainly, the ice seems relatively thin to some of us. We are also curious as to whether or not a later subsurface bloom may occur at the offshore sites since sunlight will continue to increase until 21 June and ice-cover will decrease until ~October, perhaps permitting sufficient light for phytoplankton growth to reach the uppermost halocline. As we entered deep water, we encountered the expected nutrient maxima at about 125 m associated with Bering Strait/Chukchi waters that form the upper halocline. Nutrient concentrations in this maxima appear to be a bit lower than in the past, but whether this is correlated with the recent warming and freshening of the Bering Strait inflow, or simply a normal space/time related difference between our data and past experiments will require further analysis. As is typical, dissolved silicon (silicate) was the best nutrient for tracing this maximum because this nutrient is enriched 3-4 fold in the Bering Strait waters relative to the waters supplied to the Arctic from the Atlantic. The enrichment in phosphate is less, <2, and in nitrate it is only about 1.5. In our last section, the nearshore phytoplankton bloom appeared to be stripping nutrients from the surface waters where they were regenerated at depth and transported offshore. Evidence for this is provided by the fact that we saw our highest subsurface silicate maximum in the Barrow Canyon section and by the light transmission data that suggested near surface and bottom layers that were particle rich in the inshore portion of the Barrow Canyon section with realatively clear layer in between. Approximately coincident with the nutrient maxima was an N** star minimum, and a maximum in "lignin" as determined with the Haardt fluorometer. Negative N-double star suggests an excess of the effects of denitrification over nitrogen fixation in a water parcel, and this parameter has proven to be an excellent water mass tracer with the most negative values occurring in the Pacific influenced waters and positive values occurring in waters of Atlantic origin. In general, the distribution of this parameter is as one would expect with negative values entering via Bering Strait and becoming more negative as the Pacific waters reside in the Arctic Ocean and are subjected to the effects of denitrification in arctic shelf sediments. The Atlantic Waters enter with positive values, that decrease a bit as these deeper waters reside in the Arctic. Observations in Fram Strait surface waters suggest that the Atlantic Water enters with an N** value of ~ + 2, and our data suggest that this value has decreased somewhat in the core of the Atlantic Water found during our cruise. There may be a substantial decrease in the Atlantic waters that form the lower halocline, but to calculate this, we have to sort out mixing processes between the upper and lower halocline. Results from the Haardt fluorometer may help us to do this, since the core of the maxima in these data appears to be slightly deeper than the N** mimimum. This suggests that the Haardt fluorometer maximum contains an appreciable component of waters from the lower halocline that are of Atlantic and riverine origin. Ammonium concentrations over the shelf sometimes reached concentrations of several micromolar, and distributions of Ammonium, nitrite and light transmission in our three cross-shelf sections suggest plumes of material coming off the shelf and entering the basin. Of course, the process is not strictly two dimensional as suggested by the sections, but the occurrence of such plumes in both sections suggests a mean cross-sectional transport from the shelf into the basin. In general, nitrite and urea concentrations in the water column were low, and except for one high urea concentration the water column concentrations were low and essentially within the detection limit of our method. High urea concentrations did occur, however, in some of the ice samples. Highlight Bullet Statement: Yes we did observe modification of waters over the shelf and transport of biogenic signals from the shelf to the basin on all three of our main cross-shelf sections.