Final report of Cruise NBP 06-08 (CORSACS) - November 01 to December 16, 2006
We have just arrived in Lyttleton, New Zealand and during the next couple of days we will be busy offloading equipment and preparing frozen samples for shipment back to our laboratories. Overall, the main objectives of the proposed CORSACS research were completed. Due to various circumstances, we were able to perform productive research in the Ross Sea Polynya for 16 days (out of 45 total ship days). Due to ice and weather conditions, twenty seven days (14 southbound and 13 northbound) were spent in transit to and from the polynya and 2 science days were lost in the polynya due to helo operations.
A 17 day continuous culture experiment was completed investigating the interactive effects of CO2, iron and light on algal community structure and biogeochemistry. This experiment was sampled daily and all groups participated in collecting and analyzing samples from this experiment. Preliminary data supported results from last year’s experiment and indicate that Phaeocystis antarctica had significantly higher macronutrient drawdown rates under high iron and high light conditions compared to other manipulative treatments. Based on both the low dissolved iron concentrations (ca. 0.1 nM) measured within the polynya region and the significant response of the algal community to iron additions, the prevalence of iron-limitation was observed during the spring season. A CO2 enhancement effect was also observed but it was smaller compared to the iron and light treatments.
In addition to the continuous culture experiment, numerous batch culture bioassay type experiments and semi-continuous experiments were performed to investigate the relative importance of iron, cobalt, light, temperature, CO2, vitamin B12, and UV effects on algal community structure, physiology and biogeochemistry with respect to carbon and other various elements. Preliminary results indicated that higher levels of iron, temperature and light produced the greatest response in terms of macronutrient drawdown, with respect to control conditions. Phaeocystis antarctica populations appeared to have dominated in all experiments. The relative response of diatom populations in the experiments will be determined by microscopic examination of samples transported back to various laboratories.
We also collected seawater from 74 CTD casts in the Ross Sea Polynya (including zonal transects along 76°, 76.5° and 77° S) to perform correlational analyses on the importance of various environmental parameters (temperature, salinity, macronutrients, iron, cobalt, manganese, light and CO2) on the Ross Sea algal community structure and photosynthetic efficiency as determined by quantum yields. Trace metal profiles were also performed at several stations along each transect. Levels of both dissolved and complexed cobalt and iron were measured on these samples. Due to ice conditions, only one towfish transect was performed to map sea surface trace metal concentrations. Ancillary samples and profiles from various stations were also collected for delta15N and delta13C determination, organometallic compounds, dissolved organic matter, particulate organic phosphorus, mycosporine amino acids and hydrogen peroxide measurements.
Underway sampling using the ships uncontaminated seawater pumping system was performed from the New Zealand EEZ to the Ross Sea Polynya region and back. Underway samples were collected for various analyses including algal pigments to determine community structure, quantum yield of photosynthesis, biogenic sulfur compounds (including dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO)). In addition, samples were collected to measure various enzyme activities (including carbonic anhydrase and DMSP lyase) as well as to determine expression of redox proteins (e.g. flavodoxin and ferredoxin). Continuous underway sampling of gases (oxygen, argon, DMS, CO2) was also performed throughout the cruise using a membrane inlet mass spectrometer.
Finally, eight ice coring stations were occupied and samples were collected for determination of physical properties, inorganic carbon as well as for stable isotopic measurements of delta13C and delta15N. Ice core samples were also taken for biogenic S measurements (DMS, DMSP, DMSO), algal pigment concentrations, DMSP lyase activity, and for trace metal concentrations. A workshop is planned for April 2007 to synthesize and discuss the major results from the CORSACS expeditions.
We are slowly making our way northward through the pack ice surrounding Antarctica. We left the southern Ross Sea on December 3rd and are currently scheduled to arrive back in New Zealand on Dec. 16th. The past couple of days we have performed deep CTD casts down to 4000 m to collect seawater for various chemical analyses. These represent our last CTD’s although we hope to perform two more trace metal casts when we are out of the ice (weather permitting). We were hoping to be able to collect some more ice cores on our transit north, but the ice has been very slushy and not strong enough for ice coring. We expect to be out of the ice in a day or two.
The past week has been very hectic as scientists have been very busy collecting and analyzing samples and starting their final experiments. During the last few days of November we were finally able to deploy the towfish to sample and collect trace metal clean seawater. We also completed a towfish transect along the Ross Ice Shelf. We have been very surprised this year to observe very low iron concentrations in surface waters. We had previously thought that the spring algal bloom conditions in the Ross Sea were caused by high iron concentrations in the early spring from melting sea ice. It appears from our preliminary data that the Phaeocystis populations are able to rapidly deplete the available iron in surface waters. Perhaps this is the reason that Phaeocystis populations dominate over diatoms early in the spring. Under all environmental conditions tested (including iron, light, carbon dioxide, UV, and temperature), Phaeocystis has consistently dominated the algal community over diatoms. This Phaeocystis dominance was evident even under conditions of high iron and high light; which we had hypothesized would favor diatoms.
Although our main project involved investigating climate change variables (temperature, carbon dioxide concentrations, light and iron) on algal growth, an experiment was also conducted to investigate the effects of iron and ultraviolet (UV) radiation on algal populations. Global warming does not directly affect UV levels. Ozone levels in the atmosphere are lower because man released high concentrations of chlorofluorocarbons (CFC’s) before these compounds were banned in 1987. It will take many decades for the atmosphere to rid itself of these CFC’s. While global warming can heat up the lower atmosphere, it actually acts to cool the stratosphere where ozone resides. The spring Antantarctic ozone hole is due to the very cold temperatues in the stratosphere. As a result, global warming can slow the repairing of our ozone layer. For these reasons, it is important to understand how UV can interact with other environmental parameters to affect the ecology of algal populations in the Antartctic.
November 26, 2006For the past 4 days weather conditions have improved dramatically. Temperatures have warmed to about -3 degrees C and the winds have dropped to less than 20 knots. The very thin (grease ice) and small pancake ice that has dominated our study area has finally started to melt. Today is the sunniest day we have had in the Ross Sea. It also marks the first day that we have been able to deploy the towfish and collect underway trace metal samples. For the first full day we have not been icy waters.
Yesterday afternoon we completed our west to east transect along 76.5 degrees S latitude ending at approximately 180 degrees of longitude. Today we are performing a transect to the ice shelf along 180 degree. Tomorrow we will begin a westerly transect toward Ross Island where we will rendezvous with a helicopter to off load one of our scientists to McMurdo Station to perform other experiments. To date, we have completed 55 CTD casts.
On Thanksgiving Day, we had a delicious Turkey and Ham Dinner complete with all the fixings. That evening we collected ice cores at a station about 20 miles from Beaufort Island. This day also marked the halfway point of our expedition (Hump Day). While we were on station, we were visited by Adelie and Emperor penguins. While on the ice, scientists and crew members started playing soccer, Frisbee and attempted to fly a kite (but the wind was too strong). It was a good break for all to get off the ship onto the ice for a few hours.
Tomorrow will begin our last week of sampling within the Ross Sea before our northbound voyage back to New Zealand. We will begin sampling several different experiments that are running at the same time. We will also continue our CTD survey work as well as our towfish underway sampling. Undoubtedly, this next week will represent the busiest time for all scientists.
Unseasonably cold and windy conditions continue to pound us. This morning we had to suspend all scientific operations due to 55 knot winds and 18 ft seas. We headed toward the Ross Ice Shelf for cover. We traveled east but stayed close to the ice shelf to avoid the rough sea conditions. The past few days have also been cold (-35 degrees C, wind chill) and windy (30-40 knots). We are hoping that the big wind event has opened up the polynya by pushing some of the ice to the north. At the same time, however, thin grease ice is forming. The spring phytoplankton bloom in the Ross Sea has been delayed this year because the strong winds cause the water to mix vertically. This vertical mixing of the water column means that phytoplankton are exposed to lower amounts of light to photosynthesize.
This morning we had to cancel our western most stations (near 170 degrees E) along the 77 degree S transect line. Nevertheless, we have successfully completed 30 CTD casts. We hope to complete a transect along 76.5 degrees S in the next week. But first we must collect hundreds of liters of trace metal clean seawater using our towfish pumping system. We have been unable to use this system so far because of either excessive ice conditions or because it’s so cold that the seawater freezes in the lines as it gets pumped from the ocean to our vans on deck. Tomorrow morning we will head toward the northern limit of the sea ice extent and try to tow as we head south into the wind. In this way we hope to minimize both the cold and ice conditions. However, we might also find very rough seas that far north due to the strong winds from today. If that happens, then we will steam south toward the Ice Shelf and either deploy a Zodiac to collect some clean water or perhaps do a Niskin water bottle cast for a small amount of clean water to dilute some of our experiments.
Our first set of incubation experiments will be terminated in 2 days. The phytoplankton in those bottles have used up most of the nutrients (especially nitrate). The water that we collect next will be used to set up our second (and final) set of incubation experiments that will last for about 18 days. We are hoping that weather conditions will start to warm up soon to fuel the spring phytoplankton bloom before we have to leave the study site, sometime in early December.
Based on satellite images that we had been receiving for the past week we had expected to find open water (the polynya) south of 76.5 degrees S. In scientific endeavors, however, the unexpected should always be expected. Yesterday we arrived in the polynya region only to find there was no polynya. The area was covered with pancake ice (small, round , pancake-shaped ice floes with slightly elevated edges). We decided to keep heading south toward the Ross Ice Shelf until we hit open water, expecting to find the beginning of the spring Phaeocystis algal bloom developing there. Yesterday morning we awoke to find that we had arrived at the Ross Ice Shelf but again there was no polynya present, except for open water within 1 mile of the Ice Shelf. Apparently, the strong 40 knot winds and cold temperatures (-13 degrees C) over the past week had caused the cold (-2 degrees C) seawater to refreeze. This new ice (called “grease” ice because of the thin slick sheen on the surface) was very thin and some regions had elevated fluorescence and high photosynthetic competency underneath it suggesting an actively growing algal population.
An attempt was made to collect seawater using the trace-metal clean towfish pumping system. Unfortunately, the cold conditions along the open water of the Ross Ice Shelf resulted in frozen lines. A CTD was attempted later in the day but the Niskin bottles did not fire due to a communication malfunction between the operating system and the CTD. We then steamed north to approximately 76.5 degrees S, 175 degrees E and launched a Zodiac to collect over 200 liters of trace metal clean seawater to begin incubations. This operation was successfully completed at approximately 0300 hours this morning and incubation experiments have officially started. Because of the cold weather conditions freezing up our outdoor incubators, these incubations have been started inside environmental vans under simulated sunlight conditions.
This morning we have begun our observational transect survey work along 76 degrees S. latitude. We have completed two CTD stations already today and we are currently collecting seawater using trace metal clean 10 liter Go-Flo bottles. This water will be used by Dr. Saito to begin incubation experiments investigating the importance of Vitamin B12 and iron on algal growth and community composition. Following this event we will move approximately 20 nautical miles to the east to perform another CTD cast. We will continue this transect to the east as far as the ice extent (at approximately 180 degrees). The 48 hr weather forecast is for conditions to stay cold and windy with periods of heavy snow.
For the past 5 days we have been slowly moving toward the SW. Pack ice conditions have been somewhat thicker than we anticipated and we have had to navigate through the ice without the luxury of Terrascan satellite images. The problem was fixed today when one of the 3 motors on our receiver was replaced. Currently we are at 74.3 degrees S, 179.2 degrees E and we have just completed our 6th ice sampling station under very cold (-12 degrees C) and windy (30 southerly knots) conditions. In fact, for the past 5 days the winds have remained fairly steady from the south and blowing at 25-45 knots. Although these conditions make it very cold for drilling ice cores, the drilling teams led by Prof. Rob Dunbar (Stanford) and Dr. Sedwick (BBSR) have been able to drill 5-6 cores in about an hour.
The ice cores are melted with cold filtered seawater (to prevent algal cells from breaking) and then various measurements are made including: nutrients, iron, dissolved and particulate carbon, algal pigments, microscopy samples, and for various sulfur compounds. Typically, ice algae grow throughout the ice core but they are most concentrated at the very bottom of the ice core. This region is in contact with the nutrients in seawater which allows the ice algae to grow. Ice algae also grow best at low light conditions; which further explains why they are found in the greatest abundance at the bottom of ice cores. For the past 5 days, we have not seen nightfall as we’ve entered into the spring Antarctic season with 24 hours of daylight. During the springtime, the long daylight hours begin to melt the pack ice. Ice algae will begin to break free and start to seed and grow in the water below the ice. We are now headed toward the open Ross Sea where we expect to see the beginning of the largest algal bloom in Antarctic waters that occurs every spring. This open water region (known as a polynya) should be getting bigger by the day due to the longer day length, warmer temperatures and due to ice being moved toward the north by the strong southerly winds we’ve had over the last 5 days. Scientists have only been able to get to this polynya in November since 1992, the first year that our icebreaker (Nathaniel B. Palmer) was operated. We are very fortunate indeed to have such a great vessel to conduct research. We are also privileged to work with a top notch crew (Edison Chouest) and technical support personnel (Raytheon).
Tomorrow afternoon we hope to arrive in the open water and begin collecting water for our incubations. This water collection represents the true beginning of our scientific expedition. We have been at sea for 2 weeks and are only just now beginning experiments to test our hypotheses about the effects of iron, light and carbon dioxide concentrations in affecting the algal community structure in the Ross Sea. Hopefully, the weather conditions tomorrow will allow us to deploy the towfish and begin our experiments. We eagerly await the beginning of these experiments that we designed and planned over 4 years ago.
For the past 3-4 days we have been slowly zigzagging our way south to avoid taking waves directly on the beam. A strong low pressure system to our southwest has generated gale force winds (35-45 knots) and 25-30 ft seas. A few of the new students onboard have been feeling seasick the last couple of days and virtually nobody is getting a good night's sleep. We've had to suspend all deckboard operations as waves breaking on the stern have made for dangerous conditions to work in. Nevertheless, scientists continued to make laboratory preparations for setting up incubation experiments and for calibrating various instruments. A few labs have been making various underway measurements using the ship's seawater pumping system.
This morning we finally hit the pack ice edge surrounding Antarctica at approximately 64.5 degrees S and 175 degrees E. The winds have died down to about 5 knots and the ship is riding smoothly through the thin ice (approximately 1 ft thick). At present we are breaking through ice at about 6 knots of speed. At that speed it will take us over 4 days to reach the open water polynya of the Ross Sea at about 76 degrees S. Realistically, however, we do not expect to get to the polynya for at least 5 days as we hope to complete at least 5 or 6 ice sampling stations along the way. I will describe that operation in a few days.
This afternoon we will have several test operations. Just after lunch we will send our CTD (conductivity-temperature-depth) rosette down to 1000 meters. We will test all sensors onboard the rosette as well as our ability to collect seawater at different depths using our 24- ten liter Niskin bottles attached to the rosette. Several groups will collect deep seawater that they will use as seawater blanks for various instruments. The CTD is the most vital piece of equipment on any oceanographic expedition. This CTD has new hydrowire which not only functions to send the CTD to appropriate depths but also is used to send electronic signals to close bottles at the right depths. Following the CTD cast, the trace metal group will perform a cast to flush out their trace metal clean Niskin bottles and test out the winch operations.
The latest weather forecast calls for a strong low to develop from the south. We are expecting 35 knot winds from the east within 48 hr. This system could hamper our progress through the ice as well as postpone our ice sampling studies.
We are all eager to begin collecting data from the second expedition of the CORSACS project. As last year our main objective is to study the effects of iron, carbon dioxide and light levels on algal growth in the Ross Sea. We left Lyttleton Harbour on the south island of New Zealand (43.5 degrees S, 172.6 degrees E) at 1400 hours (local time) on Nov. 1, 2006. Our equipment setup in port went smoothly with no major problems. Our voyage south to Antarctica is expected to take anywhere between 11-13 days depending on the ice conditions. We have been very lucky so far as weather conditons have been very favorable with light winds of only approximately 5-10 knots and swells of only 6-8 ft. for the first two days. However, weather conditions have started to deteriorate and gale force winds from the NNW are expected within the next 48 hrs. As of noontime on Nov 3 (local time) we are located at 51 degrees S and 176 E. We expect to reach the pack ice edge surrounding the Antarctic continent at approximately 64 degrees S. Today we begin our first scientific operations. In the afternoon, we will test our pumping system for collecting trace metal clean seawater. We call this system the towfish. Last year, the system worked beautifully and we were able to pump clean seawater from about 5 meters depth while the ship was moving at between 3 to 7 knots. Today we will test the pumping system and flush out all the lines. Biologists will also use the clean seawater that is pumped onboard to rinse out all of their incubation bottles which have been soaking in acid (so that they are trace metal clean). All the scientists have been busy over the last several days calibrating their instruments. At approximately midnight we will leave the New Zealand Exclusive Economic Zone (EEZ). Within this 200 nautical mile limit (from all NZ islands) a permit is required in order to collect seawater for analytical measurements.
Starting at midnight tonight, our group (from the Hollings Marine lab at the College of Charleston) will be collecting samples every hour (around the clock) from the ships underway pumping system. We will collect samples for the measurement of algal pigments (which we use to identify the algal species present in the water), the physiological state of the phytoplankton and various sulfur compounds that we believe are important in affecting the climate system of the Earth. We work in teams of two with 12 hr shifts so that we are continuously sampling. Tomorrow morning we will also begin our science talks. Several graduate students and post-docs will present their results from last year's cruise over the next week. Hopefully, the weather will not be too rough to listen to the talks.