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IODP Expedition 382

Iceberg Alley and Subantarctic Ice and Ocean Dynamics


Daily Science Report for 18 April 2019

Location: Hole U1536E (59°26.4496′S, 41°3.6392′W, water depth 3219.1 mbsl; proposed Site SCO-13A)

Science Update: We continued drilling Hole U1536E until we reached 312 mbsf. At 0850 h we deployed a free-fall funnel, which will enable reentry into the hole if icebergs force us to move from our location. Drilling then continued to 340 mbsf, where we planned to start coring. At 1300 h an iceberg entered the red zone, so we pulled the drill string up to ~50 mbsf and waited for the iceberg to pass. At 1700 h we resumed operations and lowered the drill string back down the hole. The bottom of the hole contained 3 m of soft fill. Cores U1536E-2R to 3R penetrated from 340.0 to 359.0 m and recovered 7.35 m (39%).

The science party met to hear a presentation about iron oxide minerals and applying them to find the provenance of ice-rafted debris and fine-grained sediments.


Daily Science Report for 17 April 2019

Location: Hole U1536E (59°26.4496′S, 41°3.6392′W, water depth 3219.1 mbsl; proposed Site SCO-13A)

Science Update: At the start of the day, the drill string was being raised to the ship; the bit reached the rig floor at 0630 h. After some rig maintenance, we made up the RCB bottom-hole assembly and lowered the drill string, reaching 37 m above the seafloor at 1730 h. We installed the top drive, and a core barrel with a center bit was pumped down. We started Hole U1536E at 2140 h with the aim to drill down without coring to 340 mbsf, just above the depth reached by Holes U1536A and U1536C. By midnight Hole U1536E was 81.5 m deep. During the day, seven icebergs were monitored and three of them had a projected closest approach of less than 5 nmi.

The science party met to hear a presentation on the Antarctic bottom water and changes in this water mass over the last two glacial terminations.


Daily Science Report for 16 April 2019

Location:
Hole U1536C (59°26.4604′S, 41°3.6191′W, water depth 3222.0 mbsl; proposed Site SCO-13A)
Hole U1536D (59°26.4501′S, 41°3.6198′W, water depth 3221.8 mbsl; proposed Site SCO-13A)

Science Update: As the day started, we were within an iceberg “red zone,” when the projected Closest Point of Approach (CPA) of an iceberg is less than 3 nmi and the time for it to reach the CPA is less than twice the time required to pull up the drill string to within 50 m of the seafloor. After the iceberg passed our location at 0700 h, we started to lower the drill string back down to the bottom of the hole to resume coring. Cores U1536C-38F to 40F penetrated from 341.4 to 352.0 mbsf and recovered 11.0 m (103%). At 1400 h, another iceberg entered the red zone, and we decided to end Hole U1536C, pull the drill string out of the hole, move 20 m north, and take a further mudline core for high-resolution pore water sampling. At 1940 h, Core U1536D-1H penetrated from the seafloor to 6.9 m. However, the core liner shattered and the core had to be pumped out of the barrel, so it could not be used for the intended purpose. At midnight, the drill string was being raised up to the ship in order to change over to the rotary core barrel (RCB) bottom-hole assembly.

Cores U1536C-29F to 40F were split and described. They consist of diatom-rich silty clay, with dropstones, and are late Pliocene to early Pleistocene in age.


Daily Science Report for 15 April 2019

Location: Hole U1536C (59°26.4604′S, 41°3.6191′W, water depth 3222.0 mbsl; proposed Site SCO-13A)

Science Update: Cores U1536C-18F to 37F penetrated from 236.4 to 341.4 mbsf and recovered 98.5 m (95%). There was a 1 m drilled interval to pass a hard layer at 292 m. In the morning, two icebergs were projected to approach within 5 nmi of the ship but they changed path and the alert was lifted. Throughout the day we continued to monitor icebergs within 25 nmi of the ship. At 2245 h an iceberg that was 6 nmi away was projected to pass within 3 nmi of the ship, so we stopped coring at that point. At midnight we were in the process of raising the drill string to 50 m below the seafloor.

Cores U1536C-12H to 28F were split and described. Cores 12H to 19H consist of greenish-gray diatom ooze with clay and silt, and Cores 20H to 28F consist of diatom-rich silty clay. Dropstones are present.


Daily Science Report for 14 April 2019

Location: Hole U1536C (59°26.4604′S, 41°3.6191′W, water depth 3222.0 mbsl; proposed Site SCO-13A)

Science Update: Hole U1536C was spot cored in order to fill gaps in the stratigraphy from Holes U1536A and U1536B. Cores 4H to 17F (and the drilled intervals 31, 91, 111, 131, and 161, which advanced 143.0 m without recovery) penetrated from 16.1 to 236.4 m and recovered 62.1 m (80%). We switched to half-length piston coring after encountering a hard layer at 225.3 m.

Cores U1536C-1H to 10H were split and described. They consist of greenish-gray diatom ooze with clay and silt, and are Pleistocene in age. Dropstones and volcanic tephra layers are present.


Daily Science Report for 13 April 2019

Location:
Hole U1536B (59°26.4608′S, 41°3.6399′W, water depth 3220.1 mbsl; proposed Site SCO-13A)
Hole U1536C (59°26.4604′S, 41°3.6191′W, water depth 3222.0 mbsl; proposed Site SCO-13A)

Science Update: Cores U1536B-15H to 25H penetrated from 121.6 to 226.1 m and recovered 108.7 m (104%). At 1130 h we started to raise the drill string because of approaching ice, which consisted of a large iceberg and a flotilla of smaller icebergs (bergy bits and growlers) that had calved from the main iceberg. At 1325 h the drill string cleared the seafloor, ending Hole U1536B.

From 1340 h we offset to avoid the small icebergs and continued to monitor the large iceberg until it passed us. Rig floor operations restarted at 1800 h and Hole U1536C was started at 2035 h. Cores U1536C-1H to 2H penetrated from the seafloor to 16.1 m and recovered 15.8 m (98%).

Cores U1536B-1H to 25H were split and described. They consist of greenish-gray diatom ooze with clay and silt, and are Pleistocene in age. Dropstones are present.


Daily Science Report for 12 April 2019

Location: Hole U1536B (59°26.4608′S, 41°3.6399′W, water depth 3220.1 mbsl; proposed Site SCO-13A)

Science Update: The iceberg that we were monitoring yesterday continued to approach the ship, and the decision was made to leave Hole U1536A when the iceberg was 1.7 nmi away. At 0130 h the drill string was raised above the seafloor and we moved about 1 nmi to the east–northeast to avoid the path of the iceberg. By 0320 h the iceberg had passed and we started to move back to Site U1536, while monitoring a second iceberg and a growler (a small iceberg the size of a truck).

At 0615 h the location was free of ice and we started lowering the drill string to the seafloor to start Hole U1536B. Cores U1536B-1H to 14H penetrated from seafloor to 121.6 m and recovered 122.0 m (100%). All cores were oriented and formation temperature measurements were made while taking Cores 5H, 8H, and 13H.

Cores U1536A-39F to 53F were split and described. They consist of diatom-rich silty clay. Dropstones are present.


Daily Science Report for 11 April 2019

Location: Hole U1536A (59°26.4602′S, 41°3.6596′W, water depth 3219.5 mbsl; proposed Site SCO-13A)

Science Update: Cores U1536A-31F to 53F penetrated from 244.0 to 354.4 m and recovered 114.3 m (104%). No cores were oriented and there were no formation temperature measurements today. An approaching iceberg was monitored in the afternoon, and by the evening it was still heading towards the area of the ship. At 2115 h the iceberg was 5.7 nmi and 5.5 h from the ship, and we followed the iceberg protocol: we stopped coring and raised the drill string up to about 50 m below the seafloor. At midnight we were standing by and monitoring the iceberg’s path.

Cores 18H to 38F were split and described. Cores 18H to 31F are mainly greenish-gray diatom ooze with clay and silt, and Cores 32F to 38F are mainly diatom-rich silty clay. Iceberg-rafted dropstones are present.


Daily Science Report for 10 April 2019

Location: Hole U1536A (59°26.4602′S, 41°3.6596′W, water depth 3219.5 mbsl; proposed Site SCO-13A)

Science Update: Cores U1536A-2H to 30F penetrated from 118.5 to 244.0 m and recovered 128.8 m (103%). Cores 14H to 23H were oriented and formation temperature measurements were taken with Cores 16H, 19H, and 22H. Cores 22H and 23H were difficult to pull out of the formation, so we switched to half-length piston coring for Cores 24F to 30F.

Cores 6H to 17H were split and described. They consist of greenish-gray diatom ooze with variable amounts of clay and silt.


Daily Science Report for 9 April 2019

Location: Hole U1536A (59°26.4602′S, 41°3.6596′W, water depth 3219.5 mbsl; proposed Site SCO-13A)

Science Update: Cores U1536A-2H to 13H penetrated from 4.5 to 118.5 m and recovered 121.3 m (102%). All piston cores were oriented and formation temperature measurements were taken with Cores 4H, 7H, 10H, and 13H. The coring line parted during the Core 13H run, so 50 m of line was cut and the core barrel was fished.

In the morning, the source in the X-ray core imager stopped working. After troubleshooting, the spare source was installed and the imager settings were recalibrated. We think that the original source had come to the end of its lifespan after usage during the instrument testing phase and on the last expedition. The X-radiographs will be used to quantify the iceberg-rafted detritus (IRD) content of the Iceberg Alley cores.

Cores U1536A-1F to 6H were split and described. They consist of diatom ooze with variable amounts of clay and silt. Sub-mm to cm-sized IRD clasts are seen in the X-ray images.


Daily Science Report for 8 April 2019

Location: Hole U1536A (59°26.450′S, 41°3.610′W, water depth 3219.5 mbsl; proposed Site SCO-13A)

Science Update: We started the day waiting for sea and weather conditions to improve, and at 0730 h we were able to restart operations. We made up the bottom-hole assembly and tested that the piston corer was landing correctly. The rest of the drill string was assembled and lowered to the seafloor. The top drive was installed by 1830 h. The first piston core run broke the shear pins mechanically before it could be shot as planned. The second piston corer was run with three shear pins in order to test that the system pressured up without problems. The third piston core was run with a half-length barrel, recovering 4.5 m (100%) in Core U1536A-1F, in a water depth of 3219.5 m. The core was almost full and the top 1.5 m of sediment was soupy, so an unambiguous mudline depth was hard to determine exactly.

The science party met to hear a presentation about carbon dioxide levels in the Pliocene and Pleistocene.


Daily Science Report for 7 April 2019

Location: Site U1536 (59°26.450′S, 41°3.610′W, proposed Site SCO-13A)

Science Update: At the start of the day, the drill string was being raised back to the ship in order to inspect the bottom-hole assembly (BHA) after the piston corer had misfired while attempting to start Hole U1536A. At 0815 h, with the bit at 77 m below the rig floor, sea conditions became too rough to continue operations and we waited on weather until 1500 h. At 1000 h we moved 500 m to the north to avoid an iceberg. The BHA was raised to the rig floor and no obstruction was found inside. Rough sea conditions returned at 1800 h and the rest of the day was spent waiting on weather.

The science party met at noon to discuss the current weather and ice conditions, and spent the day working on revisions to the site reports from Sites U1534 and U1535.


Daily Science Report for 6 April 2019

Location:
• In transit to Site U1536 (proposed Site SCO-13A)
• Site U1536 (59°26.450′S, 41°3.610′W, proposed Site SCO-13A)

Science Update: Today we completed the final 8 nmi to Site U1536 (proposed Site SCO-13A). During the previous day’s transit we had observed that the 3.5 kHz sub-bottom profile contained a series of reflections down to about 100 m below seafloor; based on this we decided to make two survey profiles over the site, each 4 nmi long along the site-survey seismic lines. The 3.5 kHz survey confirmed the water depth and provided details of the shallow reflectors at the site. The towed magnetometer had been deployed during the transit (in international waters) and was brought back to the deck after the survey. The thrusters were lowered at 0430 h, ending the sea voyage. The drill string was assembled and lowered to the seafloor. A pig (a cleaning device) was pumped down to remove rust from the inside of the drill pipe, but it did not emerge from the end of the drill string. This caused the piston corer to misfire twice, and despite deploying a barrel with a center bit to try to remove any remaining obstruction, the piston corer misfired a third time. At midnight, the drill string was being raised back to the ship in order to clear the obstruction.

The science party met to hear a presentation by the expedition’s ice observer about the US Arctic research vessel Sikuliaq and on ice monitoring during Expedition 382.


Daily Science Report for 5 April 2019

Location: In transit to Site U1536 (proposed Site SCO-13A)

Science Update: Today we travelled 229 nmi at an average speed of 9.5 kt. In midmorning we reduced speed because of icebergs in the general area and reduced visibility due to fog, but we were able to resume normal speed by late morning. At midnight we were 8 nmi from the site location.

The science party met to hear a presentation about the tectonic and paleoceanographic evolution of the Scotia Sea and its sub-basins. The scientists finalized the first drafts of the Site U1534 and U1535 reports, and sampling plans were confirmed for Site U1536.


Daily Science Report for 4 April 2019

Location: In transit to proposed Site SCO-13A

Science Update: The day was spent in transit to proposed Site SCO-13A in the Dove Basin study area. We travelled 283 nmi at average speed of 11.8 kt. The first iceberg of the expedition was spotted at 1600 h, at 56°20′S, 49°28′W. At midnight, 237 nmi of the transit remained, with an estimated time of arrival in the evening of 5 April.

The science party met to present and discuss the results from Sites U1534 and U1535. The scientists continued to write up the site reports and to make the remaining geochemical, paleomagnetic, and physical property analyses on samples from those two sites.


Daily Science Report for 3 April 2019

Location:
• Hole U1535A (53°11.4899′S, 58°45.6048′W, water depth 646.9 mbsl; proposed Site SFSD-02A)
• In transit to proposed Site SCO-13A

Science Update: Cores U1535A-15F to 17F penetrated from 102.9 to 117.3 m and recovered 11.4 m (79%). With operations completed at the Subantarctic Front sites, we started pulling up the drill string at 0330 h. We laid down the bottom-hole assembly, secured the rig floor for transit, and started the three-day sea voyage across the Southern Ocean to proposed Scotia Sea Site SCO-13A at 0848 h. Iceberg conditions in the region of Site SCO-13A are being monitored and the final decision on whether to start drilling at the site will be taken when we reach the area, which is currently classified as ice free.

Cores U1535A-1H to 17F were split and described. They consist of biosiliceous microfossil-bearing greenish-gray silty clay, and contain a comparable stratigraphy to the upper part of Site U1534.


Daily Science Report for 2 April 2019

Location:
Hole U1534D (53°11.3879′S, 58°45.6259′W, water depth ~606.1 mbsl; proposed Site SFSD-03A)
Hole U1535A (53°11.4899′S, 58°45.6048′W, water depth 646.9 mbsl; proposed Site SFSD-02A)

Science Update: We started Hole U1534D at 0045 h. Cores 1H to 3H penetrated from the seafloor to 28.5 m and recovered 29.6 m (104%). The purpose of this hole was to fill a gap in stratigraphic coverage and to provide more material for sampling in the upper part of the stratigraphy. From 0515 to 0930 h we transited 4 nmi east to Site U1535 (proposed Site SFSD-02A) in dynamic positioning mode so that we did not have to raise the drill string back to the ship. Cores U1535A-1H to 14F penetrated from the seafloor to 102.9 m and recovered 101.1 m (103%). Cores 9H to 11H were difficult to remove from the core barrel, so we switched to half-length piston coring at 88.5 m.

Cores U1534C-4H to 19H and U1534D-1H to 3H were split and described. They consist of biosiliceous microfossil-bearing greenish-gray silty clay. Because of the possible risk that foraminifer microfossils in the cores might dissolve after the cores are split (which has been observed in some high latitude sediments), samples were taken from Hole U1534C every 20 cm and stored frozen.


Daily Science Report for 1 April 2019

Location:
Hole U1534B (53°11.3763′S, 58°45.6298′W, water depth ~605.1 mbsl; proposed Site SFSD-03A)
Hole U1534C (53°11.3865′S, 58°45.6296′W, water depth 606.3 mbsl; proposed Site SFSD-03A)

Science Update: We started coring Hole U1534B at 0245 h. Core 1H recovered 1.5 m of sediment, but the core liner shattered and no clear mudline could be observed, so we decided to start a new hole. We started coring Hole U1534C at 0345 h. Cores 1H to 19H penetrated from the seafloor to 168.0 m and recovered 159.6 m (95%). Core 19H recovered 0.71 m and its core liner shattered, indicating that we had reached the limit of full-length piston coring, so we decided to stop coring Hole U1534C. Core 19H was on deck at 2135 h and at midnight we were pulling up the drill string in the hole.

Cores U1534A-31F to 47F, U1534B-1H, and U1534C-1H to 3H were split and described. They consist of biosiliceous microfossil-bearing greenish-gray silty clay.