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IODP Expedition 379

Amundsen Sea West Antarctic Ice Sheet History


Daily Science Report for 13 February 2019

Location: Hole U1532G (68°36.6954′S, 107°31. 5299′W; water depth 3961 mbsl; proposed site ASRE-08A)

Science Update: At 0115 h, we completed assembling the free-fall reentry system and then started lowering the RCB drilling assembly through the middle of the reentry system and to the seafloor. After starting Hole U1532G at 0920 h and penetrating to 51.9 m, we dropped the reentry system at 1100 h. We continued drilling without coring to 161.5 m but had to pause operations due to approaching ice from 1730 to 1815 h. After spending ~1 h clearing ice from the wireline seal (BOP) in the top drive, we resumed drilling. When the bit had reached 171.2 m at 1945 h, approaching ice forced us to pause operations again and raise the bit back up to 54 m below the seafloor. We spent the rest of the day waiting for ice to clear the area.


Daily Science Report for 12 February 2019

Location:
• Hole U1532F (68°36.6833′S, 107°31.5303′W; water depth 3961 mbsl; proposed site ASRE-08A)
• Hole U1532G (68°36.69′S, 107°31.53′W; water depth 3961 mbsl; proposed site ASRE-08A)

Science Update: After having to pull out of Hole U1532F yesterday due to ice, we continued waiting for ice to clear the area with the bit just above the seafloor. At 0900 h, we decided that due to the frequency of ice interruptions, a reentry system would be required for the multiple reentries needed to core deeply. We removed the top drive and recovered the drill string with the bit arriving back on the rig floor at 1845 h. While the drill string was being recovered, we started preparing the parts of a free-fall reentry system (casing shoe, one joint of casing, mud skirt, the outer structural parts of the hydraulic release tool, and free-fall funnel). As soon as the bit was back on board, we spent the rest of the day assembling the reentry system in the center of the moonpool beneath the rig floor.


Daily Science Report for 11 February 2019

Location: Hole U1532F (68°36.6833′S, 107°31.5303′W; water depth 3961 mbsl; proposed site ASRE-08A)

Science Update: Late yesterday, we started drilling Hole U1532F with a plan to start RCB coring at ~378 m—just above the maximum coring depth reached in Hole U1532D. Today, we continued drilling Hole U1532F without coring from 18.6 to 105.1 m, at which point we had to stop to fix a hydraulic hose in the top drive (0230–0430 h). When the bit had reached 321.4 m (at 1630 h), approaching ice forced us to stop drilling, recover the RCB core barrel with center bit, and raise the bit back up to just below the seafloor (45.5 m). We wanted to deploy a free-fall funnel, but the ice was converging on our position too quickly and there was not enough time to deploy it. We pulled the bit out of seafloor at 1921 h and spent the rest of the day waiting for ice to clear the area.


Daily Science Report for 10 February 2019

Location:
• Hole U1532D (68°36.6953′S, 107°31.5015′W; water depth 3961.5 mbsl; proposed site ASRE-08A)
• Hole U1532E (68°36.4852′S, 107°31.9608′W; water depth 3977.4 mbsl; proposed site ASRE-08A)
• Hole U1532F (68°36.6833′S, 107°31.5303′W; water depth 3960.4 mbsl; proposed site ASRE-08A)

Science Update: After waiting for ice, we deployed an RCB core barrel at 0000 h and started RCB coring in Hole U1532D. Cores U1532D-2R to 3R penetrated from 19.2 m (362.7–381.9 m) and recovered 17.42 m (91%). At 0415 h, approaching ice forced us to raise the bit back up to just below seafloor. The ice kept converging, so we pulled the bit completely out of Hole U1532D at 0605 h. Instead of waiting for the ice to pass and allow us to resume operations, we decided to move ~0.4 nmi to the northwest along the approved segment of the seismic reflection data and start a new hole. After waiting until 1130 h for ice to clear the area, we started drilling without coring in Hole U1532E, and the bit reached 101.6 m at 1445 h. Increasing winds, snow, and swell that made it difficult to visually track smaller pieces of ice (which do not show up on radar) combined with larger ice in the area made us pause operations and raise the bit up to just below the seafloor (48.6 m). Unfortunately, at 1830 h approaching ice forced us to pull the bit completely out of Hole U1532E. We raised the bit to 105 m above the seafloor, and while waiting for ice to move out of the area we conducted routine servicing of the drill line (slip and cut). We moved back near the location of Holes U1532A–U1532D and started drilling without coring in Hole U1532F at 2315 h. We plan to drill down to ~378 m and then RCB core from that depth.

Cores U1532D-2R through 3R were X-rayed manually as well as with the new automated system. These two cores consist of dark gray thinly laminated silty clay with one interbed of greenish gray silty clay with dispersed sand and granules.


Daily Science Report for 9 February 2019

Location: Hole U1532D (68°36.6953′S, 107°31.5015′W; water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: We continued drilling without coring in Hole U1532D from 78.8 to 247.2 m. At 0730 h, approaching ice forced us to raise the bit up to 55.5 m below the seafloor. The rig floor was cleared to resume operations at 1530 h and we lowered the bit back down to the bottom of the hole. At 1715 h, we dropped an RCB core barrel with a center bit and resumed drilling without coring from 247.2 m. At 2300 h, the bit reached 362.7 m and we started to recover the center bit to prepare for RCB coring.

The laboratory teams submitted their weekly reports and continued to acquire, process, and integrate results from Holes U1532A, U1532B, and U1532C.


Daily Science Report for 8 February 2019

Location: Hole U1532D (68°36.70′S, 107°31.47′W; water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: We finished recovering the drill string and APC/XCB bottom-hole assembly (BHA) with the bit arriving back on the rig floor at 0045 h. After laying out the APC/XCB specific parts of the BHA (seal bore and nonmagnetic drill collars), the drill crew started putting together the RCB BHA. Some extra time was required to fix a couple of issues identified by the routine verification of the drill collar interior diameter and core barrel space out within the BHA. From 0700 to 1430 h, we lowered the bit until it was 21.5 m above the seafloor. We then installed the top drive, deployed a center bit, and adjusted the drill string to prepare for starting Hole U1532D. Unfortunately, at 1545 h, we had to pause operations due to approaching ice. We maneuvered the ship as required to avoid the ice until it cleared the area. We were finally able to start drilling into the seafloor at 2130 h and drilled without coring from the seafloor to 74.8 m by the end of the day.

The laboratory teams presented a summary of their initial results from the first three holes at Site U1532.


Daily Science Report for 7 February 2019

Location: Hole U1532C (68°36.6952′S, 107°31.4721′W; water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: The first half of the day was spent XCB coring. Cores U1532C-28X to 33X penetrated from 338.8 to 392.3 m and recovered 45.19 m (85%). Approaching ice and diminishing visibility due to snow forced us to pause coring; Core 33X was pulled after penetrating 5.5 m. At this point, we decided to abandon further XCB coring and switch to RCB coring since (a) penetrating deeply at this is site is a primary objective and will require RCB coring, (b) RCB coring may get better quality core at the current hole depths, and (c) we wanted to take advantage of the time spent waiting for ice and environmental conditions to improve. We started recovering the drill string at 1315 h. The bit cleared the seafloor at 1520 h and we continued raising the drill string. The bottom-hole assembly (BHA) arrived at the rig floor by 2115 h and the rest of the day was spent modifying the BHA for RCB coring.

X-ray images were collected for Cores U1532C-28X to 33X, and Cores 27X to 33X were split and described. The sediments consist of relatively uniform dark gray thinly laminated silty clay with few irregularly spaced interbeds of greenish gray silty clay to sandy mud with dispersed granules and pebbles. Rare black laminae and lenses, some with a biosiliceous component, were found within the laminated silty clays.


Daily Science Report for 6 February 2019

Location: Hole U1532C (68°36.6952′S, 107°31.4721′W; water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: Just as Core U1532C-24X arrived on the rig floor at 2355 h last night, we had to stop coring again and raise the bit back up to 50.5 m due to approaching ice. At 0530 h this morning, we were able to resume operations and started lowering the bit back to the bottom of the hole. The bit encountered a bridge in the hole at 172.5 m, so we deployed an XCB core barrel with a center bit to drill through it and then washed the bit down to the bottom of the hole at 310.1 m. We circulated 25 barrels of mud to clean cuttings out of the hole and retrieved the center bit so we could resume XCB coring. Just as we were about to drop the XCB barrel, approaching ice put operations back on hold; however, this time we kept the bit near the bottom of the hole. At 1545 h, the ice moved away and we resumed XCB coring for the rest of the day. Today, Cores U1532C-25X to 27X penetrated from 310.1 to 338.8 m and recovered 25.36 m (88%).

X-ray images were collected for Cores U1532C-25X through 27X, and Cores U1532C-25X and -26X were split and described. The major lithology is thinly laminated, dark gray silty clay. Interbeds of greenish gray bioturbated and laminated mud with pebbles and granules occur, but are irregularly spaced with depth. Pebbles consist of both igneous and metamorphic lithologies, including vesicular basalt. Sand-sized olivine and green amphibole grains were identified in smear slides.


Daily Science Report for 5 February 2019

Location: Hole U1532C (68°36.6952′S, 107°31.4721′W; water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: The day started off with Cores U1532C-15F to 18F penetrating from 239.4 to 258.2 m (19.88 m recovered; 106%). We then switched to the extended core barrel (XCB) and Cores 19X to 22X penetrated from 258.2 to 291.0 m (10.18 m recovered; 31%); Cores 20X and 21X only recovered 6 cm. At 1445 h, as Core 22X arrived at the rig floor, approaching ice forced us to pause coring and raise the bit up to 50.5 m below the seafloor. We were able to resume operations at 1715 h. After lowering the bit back down to the bottom of the hole, we spent the rest of the day taking Cores 23X to 24X (291.0–310.1 m; 18.05 m recovered; 95%). Overall today, we penetrated 70.7 m and recovered 48.11 m (68%).

X-ray images were acquired for Cores U1532C-19X to 24X. Cores 11F to 23X were split and described. The major lithology is thinly laminated dark gray silty clay with interbeds of greenish gray massive and bioturbated mud with pebbles and granules. The biosiliceous component in greenish gray interbeds is highly variable. One rounded pebble (2.5 cm diameter) was identified as K-feldspar granite. For the XCB cores, slight to moderate drilling disturbance in the form of biscuits surrounded by drilling slurry is observed in the X-ray images and split cores.​


Daily Science Report for 4 February 2019

Location: Hole U1532C (68°36.6952′S, 107°31.4721′W; water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: After pulling out of Hole U1532B at 1715 h yesterday due to approaching ice, we were finally able to resume operations shortly after midnight. The ship was offset 20 m South of Hole U1532B, and at 0035 h we started drilling into the seafloor at Hole U1532C. We drilled without coring from the seafloor, and at 0415 h we had reached 178.3 m. After retrieving the core barrel that was installed during drilling, we started Half-length APC (HLAPC) coring. Core U1532C-2F (178.3–183.0 m) arrived on deck at 0630 h. It was positioned to overlap with the deepest core from Hole U1532B (Core U1532B-11F; 175.6 to 180.3 m). Cores U1532C-2F to 11F (178.3–225.3 m) were recovered, but approaching ice forced us to pause coring at ~1630 h. The barrel for Core 12F had already been deployed and had to be recovered before we pulled the bit up to 61.9 m below the seafloor. We received the approval to lower the bit back down to the bottom of the hole at 1900 h, resumed coring, and took Cores 12F to 14F (225.3–239.4 m) by the end of the day. Cores U1532C-2F to 14F penetrated from 178.3 to 239.4 m and recovered 60.94 m (100%).

X-rays were collected on Cores U1532B-2F through 18F, and Cores U1532C-2F through 11F were split and described. The sediments are dark gray thinly laminated mud interbedded with greenish gray biosiliceous mud and ooze with pebbles and granules. The overall biogenic component in all sedimentary facies is elevated in Cores U1532C-6F through 9F. The uppermost carbonate-cemented sediment was observed in the top of Section U1532C-11F-1. HLAPC core disturbance was expressed as conjugate sets of reverse faults and upward displacement of the core edges, indicating brittle deformation and shortening perpendicular to the long axis of the core. Cores U1532B-11F and U1532C-2F contained sequences of identical lithological thickness and sedimentary properties, which confirmed successful overlap of Holes U1532B and U1532C.


Daily Science Report for 3 February 2019

Location: Hole U1532B (68°36.6837′S, 107°31.4696′W; water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: We continued APC coring and recovered Cores U1532B-5H to 9H (121.6–169.1 m; with a formation temperature measurement taken with Core 7H). After recovering Core 9H, approaching ice forced us to pause coring at 0600 h and raise the bit back up to 50.5 m below seafloor. We were able to resume operations at 0900 h, so we lowered the bit back to 169.1 m and resumed coring. Core U1352B-10H was a partial stroke, with the lowermost core liner deformed and a crack that extended up the entire core liner. Core 10H recovered 6.48 m, so we advanced the bit 6.5 m and switched to half-length APC (HLAPC) coring. After Core 11F (175.6–180.3 m) was recovered, approaching ice once again forced us to pause coring at 1315 h; we raised the bit back up to 50.5 m below seafloor. Unfortunately, the ice kept converging on our location, so we eventually had to pull the bit out of the hole at 1715 h. We spent the rest of the day positioning the ship as required to avoid the drifting ice. Cores U1532B-5H to 11H penetrated from 121.6 to 180.3 m and recovered 58.7 m (105%).

X-ray images were collected from Cores U1532B-7H through 11F, and Cores 5H through 11F were split and described. Starting with Core 8H the sediment became consolidated and splitting was done by saw. Drilling disturbance was observed at the top and base of all cores. Major lithologies consisted of dark gray laminated silty clay and light greenish gray silty clay with concentrations of granules and sand. A more significant biosiliceous component was observed in smear slides of both interbedded lithologies starting with Core 9H.


Daily Science Report for 2 February 2019

Location: Hole U1532B (68°36.6837′S, 107°31.4696′W; water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: We continued adjusting our position as required to maintain a safe distance from ice until 0015 h when the drill floor was cleared to resume operations. We offset the ship 20 m to the east of Hole U1532A, and started drilling in Hole U1532B at 0125 h. We drilled from the seafloor down to 93.1 m without coring, recovered the XCB core barrel, and resumed APC coring. The first core in Hole U1532B (Core U1532B-2H) arrived on the rig floor at 0415 h. While we were taking the next core (U1532B-3H), we had to pause coring again due to approaching ice. We raised the bit up to 50.5 m below the seafloor and waited for the ice to clear from 0800 to 1515 h. We then resumed APC coring and Core U1532B-4H (112.1–121.6 m; with a formation temperature measurement) arrived on deck at 1800 h. Before it was laid out on the rig floor, approaching ice forced us to stop coring again. We raised the bit back up to 50.5 m below the seafloor and waited from 1830 until 2215 h before being able to lower the bit back to the bottom of the hole and resume coring at 2300 h. Cores U1532B-2H to 4H penetrated from 93.1 to 121.6 m and recovered 30.14 m (106%).

Cores U1532A-8H through 11H and U1532B-2H through 6H were X-rayed. Cores U1532A-7H through 11H and Cores U1532B-2H through 4H were split and described. Equivalent lithological sequences between Cores U1532A-11H and U1532B-2H were noted, indicating that a successful overlap was achieved between the two holes. Cores U1532A-8H through 10H are dominated by brown laminated silty clays interbedded with massive gray silty clay containing granule and sand-sized clasts. Dark gray diatom-bearing mud intervals are present in the upper portion of Core U1532A-11H. The lower portion of Cores U1532A-11H and U1532B-2H through 4H are dominated by dark laminated gray silty clay with silt laminae and rare pebbles, with one interbed of greenish gray bioturbated silty clay with siliceous and calcareous biogenic components in Section U1532B-2H-6.


Daily Science Report for 1 February 2019

Location: Hole U1532A (68°36.68′S, 107°31.50′W, water depth 3961.5 mbsl; proposed site ASRE-08A)

Science Update: Cores U1532A-7H to 11H penetrated from 53.1 to 100.6 m and recovered 47.86 m (101%). All APC cores were oriented and formation temperature measurements were made while taking Cores 7H (62.6 m) and 10H (91.1 m). After recovering Core 11H we had to stop coring at 0645 h due to a combination of approaching ice as well as increasing difficulty observing ice (due to fog/snow and a slight swell). We raised the bit up to 50 m below the seafloor with the intention of resuming coring in Hole U1532A after conditions improved. Instead, we had to pull out of the hole at 0930 h and raise the bit 100 m. We spent the rest of the day adjusting our position as required to maintain a safe distance from ice. After collecting X-ray images of Cores 3H through 7H to verify image quality and observe sedimentary structures, these cores were passed through the whole-round track systems. Cores U1532A-3H through 6H were split and described. The sediments consist of brown and olive silty clays with prominent foraminifer-bearing intervals down to Core 3H. Cores 4H–6H were characterized by interbedded olive brown to greenish gray silty clay and dark grayish brown clay with only rare biogenic components. Silt laminae and color banding were common. Rare pebbles, silt pockets, and dispersed sand grains were found in the silty clay intervals.