April 1, 2006
This is my last weekly report and what a week it has been. When I last wrote we were headed back into the Weddell Sea from the Firth of Tay to re-occupy our proposed site 2, which was intended to sample the Oligocene section. As we were steaming for the site location the winds increased to between 50 and 60 knots and we were forced to "ride it out" for a day, drifting in the sea ice. During the night we were blown over 20 miles off our desired ship's track. Once the storm subsided we began assessing ice conditions in our proposed Oligocene sites. We finally found open water behind a large iceberg in the area of one of the sites. We lowered pipe and just as we were preparing to drill the berg began to drift away from us at nearly a knot. Within minutes the sea ice moved into the area and we were forced to shift the site to a new location. Again, we lost our window in the sea ice. At that point we were faced with a new low-pressure system moving into the area, so we elected to seek refuge behind Seymour Island, away from the concentrated sea ice.
Our objectives in the Seymour Island area were of a technical nature, intended to address several questions about drilling and sampling sedimentary rock while stabilizing the ship in fast ice. We searched for several hours for an area with fast ice, but without success. We finally occupied a site on the eastern flank of James Ross Island and began drilling. The weather deteriorated while on the site, but the ship was able to hold station well in winds up to 45 knots and we were able to recover sedimentary rock for a long enough time to measure the rate of penetration and sampling. The rate of penetration was just under one meter per hour with about 50% recovery, but we did acquire good core.
On the morning of the 30th weather conditions seemed to be improving, so we pulled pipe and headed back out to the open shelf. Unfortunately, the front had not completely blown itself out and by evening we again found ourselves struggling in strong winds and rapidly drifting sea ice and icebergs. During this time we re-visited our Oligocene sites only to find them covered by drifting sea ice. In fact, at one point on the morning of the 31st the captain expressed concern that we were going to have problems getting out of the Weddell Sea. We steamed north and east toward Joinville Island to our final set of sites where we believed Oligocene and early Miocene strata are situated near the sea floor. In the early evening of the 31st we made our way to our preferred site and began lowering pipe. At this stage we had less that 12 hours of drilling time before we would have to head north. I must confess that I was beginning to think that we had missed our chance to sample the ever elusive Oligocene section.
Everyone on board seemed totally committed to drilling this last site, despite the fact that we have had problems in this area with maintaining holes. You can only imagine the joy we felt when our first core came to the surface and we observed lithified muddy sand in the cutter. The paleontologists onboard then presented us with the joyful news that we had indeed sampled Oligocene strata. We were able to retrieve about 3 meters of core before drifting sea ice forced us to abandon the site, just minutes before our agreed upon departure time. At one point a large iceberg threatened to cause us to abandon the site, but some very skilled ship operating by Captain Scott Dunaway bought us the time needed to reach our drilling target. There was a lot of jubilation onboard during the night and early morning and a feeling that we had in the final hours achieved one of our most important objectives. This was our home run in the bottom of the ninth.
Over the next few weeks and months we will all examine and re-examine the success of SHALDRIL. Here is my initial assessment. First, the ice conditions we encountered this year were the worst-case scenario, thick multiyear ice drifting at rates that were totally unpredicted from our knowledge of currents in the area. As a result, we did not core at any of our initial proposed sites, yet we sampled every one of our stratigraphic targets. The fact that SHALDRIL is so mobile enabled us to improvise and overcome bad weather and severe sea ice conditions and exploit alternate sites. We even had to acquire additional seismic data to locate back-up sites in areas we never expected to visit. Our longest penetration was 50 meters, but we were able to move onto location and acquire several meters of core in the most adverse of conditions. Our drill and run strategy has certainly proved viable.
The older time intervals we have sampled (latest Eocene-earliest Oligocene, Oligocene, middle Miocene, and Pliocene) are all poorly represented in the outcrop record and the SHALDRIL cores will undoubtedly reveal much about the climate and glacial evolution of the Antarctic Peninsula. We have collected two excellent, expanded Holocene records (Maxwell Bay and the Firth of Tay) that will provide regional coverage needed to better understand Holocene climate evolution. Only one Holocene site was listed in our original proposal. We were not able to core continuously a grounding zone wedge (our proposed Site 5). This simply was not possible given the limited time we had on any given station. I feel particularly bad about this because there was considerable interest in this site on the part of the glacial geology community and it was Julia Wellner's favored site. No one has worked harder than Julia to make SHALDRIL happen and she did not get her prize. But I know that Julia, Woody Wise, Steve Bohaty and Pat Manley all agree with me that we have accomplished a great deal during this cruise and we are all excited to see what the palynologists and other experts are able to learn from SHALDRIL cores.
In addition to the scientific accomplishments, we have tested the ship and the drilling and coring systems under the most adverse conditions and have gathered considerable data for planning futures SHALDRIL cruises. The ship is capable of holding station in winds up to 45 knots, our hope was to be able to maintain station in 30 knots winds. The drilling rig is capable of penetrating up to 20 meters of glacial overburden and sampling older strata within 24 hours time. Core recovery is less than we had hoped for in glacial sediments, but we never had time to really utilize the full spectrum of tools available for this type of work. Core recovery in partially lithified sedimentary material is quite good (greater than 80%). Drilling in sedimentary rock is a bit slower than we had hoped, but the information we have gathered will enable us to make realistic estimates for future SHALDRIL projects.
The ultimate assessment of SHALDRIL will come after the science is done. As for me, I think it has been a success, but I can't help but wonder just what we would have accomplished had we had a good ice year.
Enjoy your cruise.
March 24, 2006
This has been a week of ups and downs for all onboard. When I last wrote we were at our fifth site, where we recovered 13 cores that sampled the middle Miocene section. Shortly after I wrote we sheared the drill pipe and were forced to abandon the site. The cause of the problem remains uncertain, but the best explanation is that strong currents resulted in the pipe being lowered at an angle, which resulted in weakness when we began drilling. The positive side is that we did recover good core that possibly records the earliest stages of glaciation in the region.
The next site we occupied was intended to sample the upper Miocene section. We drilled to a subbottom depth of 20 meters and, while having to abandon the site due to approaching ice before reaching the Miocene section, recovered a relatively thick interval of Pliocene sandy contourites. The cores contain abundant fossil material, both microfossils and invertebrates. We all remain baffled as to the source of so much well sorted fine sand. This could imply a warm interval within the Pliocene when deltas sourced the shelf.
We drilled a second site aimed at sampling the Miocene section and at this site the bottom hole assembly broke. At this point we decided the bottom conditions (abundant gravel near the top of the hole) were responsible for the equipment failure and departed the area. So, we found ourselves sailing back south, into the sea ice. After a day of unsuccessfully searching for ice-free sites we decided to drill our Holocene site in the Firth of Tay. As it turned out, this was a good decision because the wind has been consistently in the 20 to 40 knot range for the past 24 hours. The good news is that a low pressure system is moving through the area and the winds have been consistently out of the north. So, we are hoping that this system is the one we have been waiting on to blow the ice around a bit, opening up some of our sites.
After several hours of multibeam and subbottom profiling we decided to drill a basin in the central part of the Firth of Tay where a relatively thick section of acoustically laminated sediments, estimated from seismic data to be greater than 50 meters thick, exist. The Kasten core at this site was the most organic-rich sediment I have ever encountered. When we opened the core just before breakfast the smell spread up and down the ship, damping our appetites.
We sampled to a subbottom depth of 75 meters before encountering unilithic gravels that are assumed to rest above the basement. Core recovery in the upper 20 meters was poor, due to the high water content of the sediment. Below this level we obtained about 90% recovery. We need to visit this site again and obtain a jumbo piston core of the upper 20 meters of section. The cores contain abundant organic material and macrofossils, so we are encouraged about the prospects for obtaining an excellent radiocarbon chronostratigraphy.
The wind is starting to diminish a bit, so we are planning to go back south to our Proposed Sites 2 and 3 in the early morning. In the week remaining we intend to go all out in our efforts to core Oligocene and early Miocene strata.Â
March 16, 2006
Greetings from the N B Palmer.
Much has happened in the week since I last wrote. We got a small
break in the ice and weather conditions and were able to drill a site
along the northern flank of the basin that was an alternate for our
Proposed Site 2. The objective was to sample the late Eocene/Lower
Oligocene. We drilled to a sub-bottom depth of 20.0 meters and
retrieved 6.31 meters of core after the targeted interval was
reached. Coring efforts concentrated on the lower part of the hole,
beneath the younger glacial section. The cores recovered from this
site contain muddy, very fine sand with abundant shell fragments and
dispersed organic material. The paleontologists found diatoms and
nannofossils that provide a tentative age of latest Eocene to early
Oligocene. The sediments also contain abundant benthic foraminifera.
Ice-rafted stones within the cores appear to be intra-formational in
origin, indicating sea ice rafting. Our preliminary interpretation is
that the strata at this site are inner shelf deposits.
We were very happy to find that our age model is correct, at least
for this part of the section. The carbonate material in the cores
shows little evidence of alteration, so we should be able to acquire
strontium isotope ages for the section. Also, the occurrence of
organic material leaves us optimistic that there will be sufficient
pollen and spores for palynological analysis.
We were forced to abandon Site 3 by ice floes. We steamed to another
alternate location and reached a subbottom depth of 10 m, still
within the overburden, before being pushed off the site by ice.
After a few hours of surveying the area for more alternate sites we
decided to check out ice conditions off Joinville Island, along the
northeastern edge of the James Ross Basin, north of the ice edge. We
conducted a seismic survey of the area and were delighted to discover
a thick stratigraphic section, but were not able to tie the section
to our data set to the south. We will acquire seismic data to
connect the two study areas after we complete our drilling in the
area. The area is mostly ice-free, with the exception of scattered
icebergs and sea ice. In the early morning of March 15 we lowered
pipe and began drilling our first hole at this site.
We have now been on Site 5 for over a day and have drilled to a
sub-bottom depth of 28 meters. Several problems with drilling
equipment occurred during the day, resulting in the relatively slow
rate of penetration. The drillers think that some of the problems
are related to collapse of the hole; the seafloor at this site is
covered by a gravelly lag. Despite these frustrations, the site has
proven to be well worth the effort. The paleontologists are
confident that the older deposits sampled just below the glacial
overburden are of middle to late Miocene age. Middle Miocene is the
time when the West Antarctic Ice Sheet underwent major expansion,
having advanced onto the continental shelf in the Ross Sea. Efforts
to sample middle Miocene strata on the northern side of the Antarctic
Peninsula during ODP Leg 28 were unsuccessful, so the early evolution
of the Antarctic Peninsula Ice Sheet has remained elusive. So, we
are all excited about the prospects for this area and plan to spend
the next few days sampling as much of the stratigraphic section as
possible. The seas remain calm and drifting icebergs have, thus far,
not posed a threat to our drilling efforts here.
Cheers for now,
March 9, 2006
Greetings from the N B Palmer. It is the first sunny day we have had since arriving in the Weddell Sea five days ago and spirits of all aboard are high.
Ice conditions in the northwestern Weddell Sea have, to date, been less than desirable, with 60% to 80% ice cover and persistent northerly winds that move the ice at rates of up to a knot. Until today we have had to deal with heavy fog that has at times reduced visibility to a couple of hundred meters. Our first attempt at the outer shelf site (Proposed Site 6) was aborted after reaching 7 meters depth due to ice moving over the site. As was expected for our first site, it took a while to work the bugs out of the system.
After departing Proposed Site 6 we steamed westward to Proposed Site 4 where we found a lead in the ice and began lowering pipe. Again, we were forced to move off site due to a large ice floe. We did drill to a depth of 9.24 meters before abandoning the hole. We left the drill string in the water and maneuvered to a different location, approximately 2 kilometers from the proposed site, where we found another large lead in the ice. Working in heavy fog the captain and mates did a remarkable job of avoiding large floes and we were able to remain on this station for 9 hours. We drilled to a sub-bottom depth of 52.2 meters.
Our objective at Proposed Site 4 was to sample the thick glacial section that rests above a prominent shelf-wide glacial unconformity. Our seismic stratigraphic model indicates that this section is of Miocene age and we hope to test and refine this model so that the timing of initial ice sheet grounding on the continental shelf can be constrained.
This morning we moved back to our original Proposed Site 4 where the Quaternary overburden is much thinner. Again, ice floes caused us to abandon the site after reaching a sub-bottom depth of 11.2 meters. We did recover a small amount of sediment and are awaiting results from micropaleontological analysis of the material. In the three holes close to Proposed Site 4, we recovered 6.92 meters of core, in addition to bagged samples from non-cored intervals, containing glaciomarine sediments, but have not yet been able to date the section due to a lack of microfossils.
While the ice and fog have hampered our efforts over the past four days, we are excited to learn that modifications to the drilling equipment have greatly accelerated our drill time. At one point yesterday we were drilling at rates of a meter every 5 minutes and core recovery was taking between 20 and 30 minutes. So, what we need now is a break in the ice. Our plan is to continue with the present drill and move operations until we get a low-pressure system moving into the area. That should blow the ice away from the coast and create better conditions for drilling. So, we continue to keep a watchful eye on the barometer and weather faxes.
Cheers for now,
April 15, 2005 Report
After leaving Maxwell Bay and the South Shetlands, the NB Palmer crossed the Bransfield Strait and headed towards the Antarctic Peninsula. A short seismic survey was conducted off of the Trinity Peninsula region, just outside of Antarctic Sound, to help select alternate drill sites in case ice prevented drilling at the primary sites. Deployment of the air guns and single-channel streamer went very smoothly and high-resolution seismic was collected for a few hours. The NBP then entered Antarctic Sound at dawn and crossed into the Weddell Sea with spectacular scenery around us.
Winds in the northwestern Weddell Sea were very high when the Palmer first entered the area, sometimes reaching 70 knots. Since the ship couldn't hold station, the derrick couldn't compensate for the heave of the ship, and nobody could do much work on the deck in such conditions, seismic gear was again deployed. Seismic data was collected just to the north of the pre-selected drill sites in anticipation of having to have alternate sites planned as the ice edge was advancing north. The high winds coming from the south dispersed the ice to the north, making more of the study area ice-covered. Eventually, it became too icy to continue seismic operations. We then headed to Herbert Sound, on the north side of James Ross Island, to seek a protected area in which to resume drilling.
Herbert Sound was surveyed in 1991 and good seismic coverage is available for the area. In preparation for SHALDRIL, the data was re-analyzed to help look for alternate sites. Core analysis showed that carbonate material was present to the base of the piston cores, suggesting that material might be present at greater depths and that the entire Holocene could be dated in the region. Site NBP0502-2 includes two kasten cores, each of which reached depths of over 3 m, and one drill core that reached 10.5 m (recovery 73%). The sediment sampled is primarily diatomaceous muds with bivalves throughout and increasing terrigenous material down core. The hole bottomed out in a basaltic cobble within a diamicton unit. Because the weather had cleared at the primary sites, the hole was abandoned rather than switching sampling tools that would have allowed it to be continued.
Site NBP0502-3 was begun off of Seymour Island and was intended to sample the pre-glacial Cenozoic section that was identified as a SHALDRIL target (proposal site 2). The NBP went onto position in light ice conditions and continued to hold station as the ice increased. The ability of the ship to hold station in ice and wind has proven to be much greater than previously assumed. Position was held despite thickening ice and cover reached 8/10. A total depth of 20.74 m was reached in the hole before progress stopped. The Cenozoic section was not reached, but much was learned from the site. Besides proving that DP is possible in ice, the drillers were able to learn more about getting through glacial sediments. The lessons from NBP0502-3 have already lead them to develop some modified tools on board that will soon be tried.
After abandoning the hole off of Seymour Island, the ice was re-assessed. All involved felt that the ice was rapidly thickening and that another hole would not be possible in the area. Site 4 was selected on the seismic data collected a few days before in the Bransfield Basin. A short kasten core was collected at the site and recovered gravelly sands. Drill pipe was run almost all the way through the water column to the sea floor before the winds unexpectedly increased. Again, the NBP held station remarkably well. However, the wind quickly generated enough sea that the vessel was heaving beyond the capabilities of the drilling rig's heave compensator. Pipe had to be pulled and the site abandoned before touching the mudline.
The next drill sites will be located in the protected waters of Gerlache Strait. While protected from ice and weather, we will devote a few days to testing our capabilities to not only drill but also to sample glacial diamicton.
April 7, 2005 Report
NBP0502 (SHALDRIL) sailed from Punta Arenas on 31 March after an impressive port call. The years of preparation for SHALDRIL finally came together as we saw Seacore mount a drilling rig onto the deck of the Palmer. The detailed plans that had been made at countless meetings appeared worth it as the drilling equipment was fit onto the vessel without any room to spare yet also without major difficulty. During the port call the maximum load line on the Palmer was repainted and recertified, making the ballasting work done in February official and allowing the SHALDRIL loads to be put onto the vessel safely.
Ice imagery of the northwestern Weddell Sea indicated that the primary drill sites had significant ice cover. While the sites remained accessible by the Palmer, the likelihood of being able to hold station long enough to drill seemed unlikely, especially when the dynamic positioning system is being tried for the first time. An alternate site in Maxwell Bay, on the south side of King George Island and the largest bay in the South Shetland Islands, was thus selected to be the first drill site and will likely replace the Vega Drift site in the SHALDRIL drilling portfolio. Maxwell Bay was surveyed during DF86 and PD91 and seismic data are available from both cruises. The subpolar setting of the Maxwell Bay site ensures that the Holocene climate record that should be obtained from the core will complement the available data on Holocene climate that have been obtained farther south on the Antarctic Peninsula. 3.5 kHz data collected during this cruise, along with the deeper penetrating seismic data from the past cruises, indicate a thick succession (~100 m) of layered sediments.
The NBP reached Maxwell Bay early on the morning of 04 April. A short multibeam and 3.5 kHz survey was conducted to further characterize the drill site. The vessel started dynamic positioning just before dawn. By the end of the hole, position had been held for over 72 hours with no excursion over about 3 m. Conditions were good for most of this period but at one point winds did reach 30 knots while the vessel continued to hold station.
Drilling operations were begun on the morning of the 4th and ran smoothly until completion of the hole. The drill site is in 488 m of water and running pipe to the mud line took about 12 hours. Coring operations lasted about 48 hours and the hole reached a total depth of 108.2 m. Pulling pipe from the hole took another 12 hours or so. All cores were taken with an extended core barrel push sampler. Most sections attempted were 2.5 m in length; 1.5 m and 3 m runs were also made. Recovery for most coring runs was extremely high, averaging over 90%. Only one 2.5 m push had no recovery at all. Initial analysis of physical properties suggests that very little material was lost between core sections, at least in the upper sections. Processing of core included multisensor core logger, photographry, lithologic description, physical properties measurements, and paleontological analysis of smear slides. With the exception of the P-wave logger, everything has worked smoothly.
The section cored consists of diatomaceous sediments interlayered with fine grain ash deposits, and increasing amounts of terriginous sediment down core. The core is highly bioturbated in some sections and includes brittle stars, pelecypods, echinoderms, and one large fish vertebra among others. Benthic forams are concentrated in some zones. All samples examined contain well-preserved and diverse diatom assemblages. With the exception of a few rare reworked specimens, all diatom taxa observed throughout the section are modern (extant) species, supporting a presumed Holocene age of the core. Diatom biostratigraphy cannot differentiate between the Holocene and the late Pleistocene, but the absence of Rouxia spp. in all samples indicates an age younger than 140 Ka (Marine Isotope Stage 6) for the entire section. The core bottomed out in a soft, gray diamicton with relatively few large grains. This unit is presumed to represent the last glacial maximum but further analysis and isotopic dating is needed to confirm this.
Today, 07 April 2005, the NBP is leaving Maxwell Bay and sailing for the south side of Bransfield Basin. A short seismic survey will be conducted there to help plan for alternate sites in case the Weddell Sea sites remain inaccessible. At dawn tomorrow, we will pass through the Antarctic Sound and enter the Weddell Sea. At that point we will judge between drilling in the ice conditions that surround the primary sites and returning to the south Bransfield area to drill the alternate sites that are ice-free but potentially in worse seas.
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