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IODP Expedition 403

Eastern Fram Strait Paleo-Archive

Daily science report for 25 July 2024

Location:

  • Hole U1623E (76°31.8573′N, 12°34.4499′E; water depth 1707.2 m)
  • Hole U1623F (76°31.8565′N, 12°34.4501′E; water depth 1706.8 m)
  • Hole U1623G (76°31.8694′N, 12°34.4465′E; water depth 1704.9 m)

Science Update: Hole U1623E was spudded at 0238 h. Core U1623E-1H did not recover a good mudline, with 9.63 m of sediment, thus it was decided to abandon the hole. The vessel was moved 5 m and Hole U1623F was spudded at 0323 h. Core U1623F-1H recovered a good mudline and 6.02 m of sediment, placing the seafloor depth at 1706.8 mbsl. Cores U1623F-1H to 22F were retrieved from 0 to 162.3 mbsf, the final depth of the hole. The cores became increasingly softer and suffered from more gas expansion than cores at the same depth in neighboring holes. In addition, the drillers noticed complete loss of weight on the drill string. It was determined that Hole U1623F must have been drilled at an angle and ultimately penetrated a previously drilled hole. Thus, the decision was made to end Hole U1623F. A total of 147.04 m of sediment was recovered in Hole U1624F (91%). The drill string was pulled up, the bit cleared the seafloor at 2105 h, and the vessel was moved 20 m at a bearing of 22° from Hole U1623C . Hole U1623G was spudded at 2245 h. Core U1623G-1H recovered a mudline and 8.03 m of sediment, placing the seafloor depth at 1704.9 mbsl. Cores U1623G-1H to 3H were retrieved from 0 to 27.0 mbsf.

Cores U1623F-1H to 22F were run through the whole-round physical properties track systems, and Cores U1623F-1H to 9H were split and described. The cores predominantly consist of soft, structureless gray to greenish gray silty clay with isolated intervals of dark reddish gray and brown sandy mud and sandy patches. Dispersed clasts are present in most cores.

Daily science report for 24 July 2024

Location:

  • Hole U1623D (76°31.8554′N, 12°34.4722′E; water depth 1715.6 m)
  • Hole U1623E (76°31.8573′N, 12°34.4499′E; water depth 1707.2 m)

Science Update: Cores U1623D-52X to 56X were retrieved from 338.4 to 370.0 mbsf, the final depth of the hole. A total of 351.06 m of sediment was recovered in Hole U1624D (95%). In preparation for downhole logging, the pipe was pulled from the hole with the bit positioned at a depth of 94.8 mbsf. The triple combo tool string was rigged up by the Schlumberger Engineer and was deployed at 1230 h. Two successful passes (one main pass) of the triple combo reached a depth of 249.8 mbsf, indicating an obstruction that the tools were unable to pass was encountered at a depth of 249.8 mbsf. The seafloor was detected at about 1707 mbsl, 10 m off from the mudline core. The seismic plots of the area hint at a small trough that Hole U1624D might have been drilled in, thus the difference in seafloor depth might have been caused by a cuttings-mount that filled up the depression and was detected by the logging tools. Following the triple combo, the FMS-sonic string was rigged up and deployed at 1800 h. Two successful passes of the FMS-sonic string reached a depth of 249.8 mbsf. Logging continued until 2300 h, when the FMS-sonic string was rigged down. The drill string was pulled up, the bit cleared the seafloor at 2331 h, and the vessel moved to the coordinates of Hole U1623E.

Cores U1623D-48X to 56X were run through the whole-round physical properties track systems, and Cores U1623D-41X to 56X were split and described. The cores predominantly consist of firm, structureless gray to dark gray silty clay with dispersed to abundant clasts and several layers that contain authigenic iron sulfide grains. Several cores contain gray to reddish gray diamictons that become more common downhole.

Daily science report for 23 July 2024

Location: Hole U1623D (76°31.8554′N, 12°34.4722′E; water depth 1715.6 m)

Science Update: Cores U1623D-32X to 51X were retrieved from 193.4 to 338.4 mbsf. Coring operations were paused between 0330 h and 0500 h while the core winch depth indicator was repaired.

Cores U1623D-26F to 47X were run through the whole-round physical properties track systems, and Cores U1623D-15F to 40X were split and described. The cores predominantly consist of firm, structureless gray silty clay with dispersed intervals of reddish gray sandy mud. Isolated clasts are present in most cores.

Daily science report for 22 July 2024

Location: Hole U1623D (76°31.8554′N, 12°34.4722′E; water depth 1715.6 m)

Science Update: The bit was lowered to 1703.5 mbsl and the APC barrel was deployed. An empty core barrel was retrieved; the bit was lowered to 1709.0 mbsl and Hole U1623D was spudded at 0108 h. Core U1623D-1H recovered a good mudline and 2.28 m of sediment, placing the seafloor depth at 1715.6 mbsl. Cores U1623D-1H to 31X were retrieved from 0 to 193.4 mbsf. To offset gaps between Holes U1623A, U1623C, and U1623D for the purpose of stratigraphic correlation, Core U1623D-3F was advanced with the HLAPC.

Cores U1624D-1H to 25F were run through the whole-round physical properties track systems, and Cores U1623D-1H to 14F were split and described. The cores predominantly consist of gray, structureless silty clay that increases in compaction and firmness downhole. Intervals of sandy mud, sandy patches, and clasts are present in some cores and become more prevalent in the lower part of the described interval. All scientists met for a 1.5 h meeting to discuss how their research plans evolved since the start of the expedition.

Daily science report for 21 July 2024

Location:

  • Hole U1624C (77°35.2543′N, 10°5.6072′E; water depth 1319.6 m)
  • Underway to Site U1623
  • Hole U1623D (76°31.8560′N, 12°34.4719′E; water depth 1815.6 m)

Science Update: Cores U1624C-37X to 43X were retrieved from 217.1 to 258.0 mbsf, the final depth of the hole. A total of 240.24 m of sediment was recovered in Hole U1624C (93%). The drill string was pulled up, and the bit cleared the seafloor at 0751 h and the rig floor at 1115 h. The vessel switched from DP to cruise mode and was underway to Site U1623 at 1121 h, ending Site U1624. The vessel completed the 71.6 nmi transit at 1824 h in 4.8 h at an average speed of 10.5 kt. At 1844 h, the vessel was under full DP control. An APC/XCB BHA was assembled and lowered starting at 1846 h.

Cores U1624C-23X to 43X were run through the whole-round physical properties track systems and Cores U1624C-12F to 43X were split and described. The cores predominantly consist of firm structureless silty clay and sandy mud with dispersed to abundant clasts and isolated diamictons. Starting at Core 37X, all cores consist of structureless muddy diamictons.

Daily science report for 20 July 2024

Location:

  • Hole U1624B (77°35.2625′N, 10°5.6399′E; water depth 1319.8 m)
  • Hole U1624C (77°35.2543′N, 10°5.6072′E; water depth 1319.6 m)

Science Update: The bit cleared the seafloor at 0022 h and the vessel was offset by 20 m at a bearing of 225°. After minor maintenance on the core winch line, Hole U1624C was spudded at 0241 h. Core U1624C-1H recovered 9.2 m of sediment, placing the seafloor depth at 1319.6 mbsl. Cores U1624C-1H to 36X were retrieved from 0 to 217.1 mbsf.

Cores U1624B-40X to 45X and U1624C-1H to 22X were run through the whole-round physical properties track systems, and Cores U1624B-29X to 45X and U1624C-1H to 11F were split and described. The cores described from Hole U1624B predominantly consist of firm, structureless gray silty clay intercalated with muddy diamictons. The lower three cores entirely consist of firm, muddy diamictons with a very high abundance of clasts. The cores described from Hole U1624C predominantly consist of soft structureless gray to greenish gray silty clay with dispersed patches of sandy mud to sand that increase in compaction and firmness downhole. Dispersed to abundant clasts occur in all cores.

Daily science report for 19 July 2024

Location: Hole U1624B (77°35.2625′N, 10°5.6399′E; water depth 1319.8 m)

Science Update: Cores U1624B-19F to 45X were retrieved from 121.7 to 258.0 mbsf, the final depth of the hole. To improve recovery, Cores U1624B-25X to 45X were advanced by 5 m. Starting around 0700 h, several of the ship’s laboratory computers were affected by the global CrowdStrike issue and went into a permanent boot loop (blue screen). At 0815 h, the computer analyzing the gas safety headspace samples was affected too, thus coring was halted until 1015 h, when the Marine Computer Specialists (MCS) could break the boot loop and get the headspace computer up and running again. Throughout the day the MCSs and JRSO staff recovered all computers and servers. A total of 223.09 m of sediment was recovered in Hole U1624B (86%). The drill string was pulled up starting at 2245 h.

Cores U1624B-8H to 39X were run through the whole-round physical properties track systems and Cores U1624B-8H to 28X were split and described. The cores predominantly consist of gray to greenish gray silty clay intercalated with short intervals of clayey silt and sandy mud. Clasts of different lithologies are common to abundant in most cores.

Daily science report for 18 July 2024

Location:

  • Hole U1624A (77°35.2627′N, 10°5.6277′E; water depth 1319.8 m)
  • Hole U1624B (77°35.2625′N, 10°5.6399′E; water depth 1319.8 m)

Science Update: The vessel completed the transit to Site U1624 (proposed Site ISD-01C) at 0600 h in 6.1 h at an average speed of 11.8 kt. The drill string was lowered again and Hole U1624A was spudded at 1100 h. Upon recovery, water pressure in the liner pushed the recovered sediment onto the rig floor. The decision was made to terminate the hole and to move the vessel 5 m east. Hole U1624B was spudded at 1140 h. Core U1624B-1H recovered a good mudline and 4.09 m of sediment, placing the seafloor depth at 1319.8 mbsl. Cores U1624B-1H to 18F were retrieved from 0 to 121.7 mbsf. Formation temperature measurements were collected with the APCT-3 tool on Cores U1624B-4H, 7H, 10H, and 14F.

Cores U1624A-1H and U1624B-1H to 7H were run through the whole-round physical properties track systems and were split and described. The cores of both holes predominantly consist of soft structureless gray and greenish gray to brown silty clay with dark patches and dispersed clasts.

Daily science report for 17 July 2024

Location:

  • Hole U1623C (76°31.8594′N, 12°34.4276′E; water depth 1706.4 m)
  • In transit to proposed Site ISD-01C (Site U1624)

Science Update: Cores U1623C-53X to 55X were retrieved from 343.3 to 369.0 mbsf, the final depth of the hole. A total of 322.38 m of sediment was recovered in Hole U1623C (87%). In preparation for downhole logging, the pipe was pulled from the hole with the bit positioned at a depth of 65.5 mbsf. The triple combo tool string was rigged up by the Schlumberger Engineer and was deployed at 0830 h. An obstruction that the tools were unable to pass was encountered in the pipe at a depth of 7 mbsf. The triple combo string was pulled up and rigged down at 1200 h. The mud pumps were run at 1800 psi, the obstruction was cleared, and a deplugger was run down the pipe at 1345 h. The triple combo was rigged up again and deployed, but encountered an obstruction at the bit. Clearing the obstruction was not possible, thus the logging tools were pulled up again and were rigged down by 1815 h. The drill string was pulled up, and the bit cleared the seafloor at 1830 h and the rig floor at 2050 h. The rig floor was secured for transit and the vessel was switched from DP mode to cruise mode at 2319 h, ending Hole U1623C and Site U1623. The vessel began its passage to proposed Site ISD-01C (Site U1624) at 2336 h and completed 4.8 nmi of the 76.1 nmi transit by the end of the day at an average speed of 12 kt.

Cores U1623C-49X to 55X were run through the whole-round physical properties track systems and Cores U1623C-44X to 55X were described. The cores predominantly consist of firm, structureless gray to light greenish gray silty clay with intervals of muddy diamictons and sandy mud. Clasts are present in all cores and range from dispersed to abundant.

Daily science report for 16 July 2024

Location: Hole U1623C (76°31.8594′N, 12°34.4276′E; water depth 1706.4 m)

Science Update: Cores U1623C-33X to 52X were retrieved from 192.8 to 343.3 mbsf. All cores were advanced by 8 to 8.5 m to allow for gas expansion.

Cores U1623C-27F to 48X were run through the whole-round physical properties track systems and Cores U1623C-11F to 43X were described. The cores predominantly consist of gray silty clay with occasional patches or layers of mud or sandy mud. Sediment compaction is noticeably increasing downhole. Clasts are present in all cores and range from dispersed to abundant.

Daily science report for 15 July 2024

Location:

  • Hole U1623A (76°31.8394′N, 12°34.3985′E; water depth 1707.7 m)
  • Hole U1623B (76°31.8500′N, 12°34.4118′E; water depth 1707.7 m)
  • Hole U1623C (76°31.8594′N, 12°34.4276′E; water depth 1706.4 m)

Science Update: The bit cleared the seafloor at 0011 h and the vessel was offset by 20 m at a bearing of 22°. Hole U1623B was spudded at 0238 h. Core U1623B-1H recovered only 0.05 m of mostly unconsolidated gravel. Thus, a good mudline was not obtained and the decision was made to terminate Hole U1623B. The vessel was offset by 20 m at a bearing of 22°. Hole U1623C was spudded 0333 h. Core U1623C-1H recovered a good mudline and 9.26 m of sediment, placing the seafloor depth at 1706.4 mbsl. Cores U1623C-1H to 32X were retrieved from 0 to 192.8 mbsf. To offset gaps between Holes U1623A and U1623C for the purpose of stratigraphic correlation, Core U1623C-18X was advanced by 7 m and Cores 31X and 32X were advanced by 5 m.

Cores U1623A-50X and 51X and U1623C-1H to 26F were run through the whole-round physical properties track systems (Core U1623B-1H was not suitable for logging), and Cores U1623A-45X to 51X, U1623B-1H, and U1623C-1H to 10F were split and described. The cores described from Hole U1623A predominantly consist of alternating intervals of silty clay, clayey silt, sandy mud, and muddy diamictons. Clasts are present in all cores and range from dispersed to abundant. Core U1623B-1H consists of silty clay and very abundant clasts of multiple lithologies. The cores described from Hole U1623C predominantly consist of soft, structureless silty clay that include several intervals of sandy mud. Clasts are present in all cores and range from dispersed to abundant. In addition, Cores U1623C-11F to 14F were sampled for high-resolution sedaDNA.

Daily science report for 14 July 2024

Location: Hole U1623A (76°31.8394′N, 12°34.3985′E; water depth 1707.7 m)

Science Update: Cores U1623A-36X to 51X were retrieved from 226.0 to 369.3 mbsf, the final depth of the hole. A total of 330.72 m of sediment was recovered in Hole U1623A (90%). The drill string was pulled up starting at 2200 h.

Cores U1623A-31X to 49X were run through the whole-round physical properties track systems, and Cores U1623A-22F to 44X were split and described. The cores predominantly consist of firm, mostly structureless gray silty clay with isolated patches of sandy mud. Clasts are present in most cores and range from dispersed to abundant.

Daily science report for 13 July 2024

Location: Hole U1623A (76°31.8394′N, 12°34.3985′E; water depth 1707.7 m)

Science Update: Cores U1623A-7H to 35X were retrieved from 48.2 to 226.0 mbsf. Formation temperature measurements were collected with the APCT-3 tool on Cores U1623A-7H, 10H, and 13F. Cores U1623A-30X to 35X were advanced by 8 m to allow for gas expansion.

Cores U1623A-2H to 30X were run through the whole-round physical properties track systems, and Cores U1623A-1H to 21F were split and described. The cores predominantly consist of silty clay with smaller intervals of silt and sandy mud. Firmness is increasing noticeably downhole beginning in the middle of the described interval. Dispersed to common clasts are present in most cores.

Daily science report for 12 July 2024

Location:

  • Hole U1622A (76°27.4495′N, 12°33.2859′E; water depth 1707.5 m)
  • Hole U1623A (proposed Site BED-02B; 76°31.8394′N, 12°34.3985′E; water depth 1707.7 m)

Science Update: Lowering the drill string continued after arrival on site. Hole U1622A was spudded at 0044 h. Core U1622A-1H recovered a good mudline and 2.81 m of sediment, placing the seafloor depth at 1707.5 mbsl. Cores U1622A-1H to 7F were retrieved from 0 to 46.5 mbsf, the final depth of the hole. All cores contained more glacial debris (pebble- and cobble-sized) than anticipated, which led to a review of the site coordinates. It was determined that the site coordinates for proposed Site BED-02B were incorrect and Site U1622 is ~8 km from the approved shot point on the seismic line CAGE21-1HH-05. Hole U1622A reached a maximum penetration of 46.5 mbsf and recovered 46.48 m of sediment (99% recovery). Formation temperature measurements were collected with the APCT-3 tool on Cores U1622A-4H and 7F. The drill string was pulled up with the bit clearing the seafloor at 1305 h, and the vessel began the 4.4 nmi transit in DP mode to Site U1623 (proposed Site BED-02B), ending Site U1622. During transit, the correct coordinates for the approved shot point were determined, and following EPSP approval the vessel moved to proposed Site BED-02B. The vessel completed the transit at 1800 h in 4.8 h at an average speed of 0.92 kt. The drill string was lowered again and Hole U1623A was spudded at 1920 h. Core U1623A-1H recovered a good mudline and 3.58 m of sediment, placing the seafloor depth at 1707.7 mbsl. Cores U1623A-1H to 6H were retrieved from 0 to 48.2 mbsf. Formation temperature measurements were collected with the APCT-3 tool on Core U1623A-4H.

Cores U1622A-1H to 7F and U1623A-1H were run through the whole-round physical properties track systems, and Cores U1622A-1H to 7H were split and described. The cores predominantly consist of dark gray silty clay to dark brown sandy mud with common to abundant pebble- to cobble-sized clasts in all sections, indicative of a glacial debris flow.

Daily science report for 11 July 2024

Location:

  • Hole U1621C (76°31.3152′N, 12°44.3552′E; water depth 1635.9 m)
  • Hole U1622A (76°27.4500′N, 12°33.2833′E [peliminary]; water depth 1707.6 m)

Science Update: Cores U1621C-17H to 28X were retrieved from 140.9 to 207.9 mbsf, the final depth of the hole. Gravel and larger loose rocks began clogging up the cutting shoe in Cores U1621C-27X and 28X, leading to poor recovery. Thus, the decision was made to terminate the hole. Hole U1621C reached a maximum penetration of 207.9 mbsf and recovered 195.18 m of sediment (94% recovery). The drill string was pulled up with the bit clearing the seafloor at 1415 h and the vessel began the 4.6 nmi transit in DP mode to Site U1622, ending Site U1621. An APC/XCB BHA was assembled and lowered to the seafloor during the DP move at 2330 h. The vessel completed the transit at 0012 h on 12 July in 9.6 h at an average speed of 0.5 kt.

Cores U1621C-12H to 27X (28X was not suitable for logging) were run through the whole-round physical properties track systems, and Cores U1621C-1H to 28X were split and described. The cores predominantly consist of soft, structureless gray to tan clayey silt in the top of the hole. Compaction increases downhole to firm, structureless silty clay beginning in the transition from Core U1621C-14H to 15H. Dispersed to abundant clasts are present in most cores. Core U1621C-28X consist of cobble-sized rocks of different lithologies; the finer matrix was probably lost during coring.

Daily science report for 10 July 2024

Location:

  • Hole U1621B (76°31.3053′N, 12°44.3358′E; water depth 1636.5 m)
  • Hole U1621C (76°31.3152′N, 12°44.3552′E; water depth 1635.9 m)

Science Update: Cores U1621B-29X to 33X were retrieved from 191.1 to 216.1 mbsf, the final depth of the hole. Gravel and larger loose rocks began clogging up the cutting shoe in Cores U1621B-32X and 33X, leading to poor recovery. Thus, the decision was made to terminate the hole. Hole U1621B reached a maximum penetration of 216.1 mbsf and recovered 203.39 m of sediment (94% recovery). The drill string was pulled up, the bit cleared the seafloor at 0812 h, and the vessel was moved 20 m at a bearing of 22°. Hole U1621C was spudded at 1012 h. Core U1621C-1H recovered a good mudline and 1.49 m of sediment, placing the seafloor depth at 1635.9 mbsl. To offset gaps between holes for the purpose of stratigraphic correlation, Core U1621C-2F was shot using the HLAPC. Cores U1621C-1H to 16H were retrieved from 0 to 140.9 mbsf.

Cores U1621B-26X to 33X and U1621C-1H to 11H were run through the whole-round physical properties track systems, and Cores U1621B-20F to 33X were split and described. The cores predominantly consist of firm, structureless gray silty clay with intervals of sandy mud and muddy diamictons. Clasts are abundant to common. Cores U1621B-32X and 33X consist of sandstone, mudstone, quarzite, and plutonic rock cobbles; the finer matrix was probably lost during coring.

Daily science report for 9 July 2024

Location: Hole U1621B (76°31.3053′N, 12°44.3358′E; water depth 1636.5 m)

Science Update: Cores U1621B-5H to 28X were retrieved from 37.4 to 191.1 mbsf. To offset gaps between Holes U1621A and U1621B for the purpose of stratigraphic correlation, Core U1621B-7F was shot using the half-length APC (HLAPC). Additionally, the HLAPC was used for Cores U1621B-11F to 13F to target an interval of poor recovery in Hole U1621A. An APC core was attempted with Core U1621B-14H, but it was a partial stroke. The HLAPC was deployed for Cores 15F–20F and the XCB system was used for Core 21X to facilitate a 2.5 m advance for correlation. Another HLAPC core was attempted with Core 22F, but it was a partial stroke, thus XCB coring continued from Core U1621B-23X on.

Cores U1621B-1H to 25X were run through the whole-round physical properties track systems, and Cores U1621B-1H to 19H were split and described. The cores predominantly consist of soft, structureless silty clay that increases in compaction and firmness downhole. Several cores contain reddish-brown patches of sandy mud and dispersed to abundant clasts.

Daily science report for 8 July 2024

Location:

  • Hole U1621A (76°31.2956′N, 12°44.3175′E; water depth 1638.6 m)
  • Hole U1621B (76°31.3058′N, 12°44.3377′E [preliminary]; water depth 1636.5 m)

Science Update: Cores U1621A-17H to 28X were retrieved from 126.6 to 215.3 mbsf, the final depth of the hole. Headspace gas C1/C2 ratios were monitored for safety and were in the normal range. Gravel and larger loose rocks began clogging up the cutting shoe in Cores U1621A-27X and 28X, leading to poor recovery. The drill crew also noticed about 3 m of infill at the bottom of the hole that they were unable to remove. Thus, the decision was made to terminate the hole. Hole U1621A reached a maximum penetration of 215.3 mbsf and recovered 180.4 m of sediment (84% recovery). The drill string was pulled up with the bit clearing the seafloor at 1745 h, and the vessel was moved 20 m at a bearing of 22°. After minor maintenance on the core winch line, Hole U1621B was spudded at 2038 h. Core U1621B-1H recovered a good mudline and 8.9 m of sediment, placing the seafloor depth at 1636.5 mbsl. Cores U1620A-1H to 4H were retrieved from 0 to 37.4 mbsf.

Cores U1621A-8H to 27X (28X was not suitable for logging) were run through the whole-round physical properties track systems, and Cores U1621A-5H to 28X were split and described. The cores predominantly consist of soft, structureless silty clay that increases in compaction and firmness downhole. Several cores contain reddish-brown patches of sandy mud and white quartz-sand. Core U1621A-27X recovered a sandy diamicton with a large plutonic clast at its base. Core U1621A-28X recovered no fine sediments as these were most likely lost during the coring process, but only recovered gravel to pebble-sized clasts of varying lithologies.

Daily science report for 7 July 2024

Location:

  • In transit to proposed Site BED-01A (Site U1621)
  • Hole U1621A (76°31.2956′N, 12°44.3175′E; water depth 1638.6 m)

Science Update: The vessel arrived on Site U1621 at 0726 h and switched from cruise mode to DP mode, starting the site. The 138 nmi voyage was completed in 11.5 h at an average speed of 12 kt. An APC/XCB BHA was made up and lowered to the seafloor. Hole U1621A was spudded at 1315 h. Core U1621A-1H recovered a good mudline and 0.79 m of sediment, placing the seafloor depth at 1638.6 mbsl. Cores U1621A-1H to 16H were retrieved from 0 to 126.6 mbsf. The XCB was deployed for Cores 11X–14X due to gas expansion of the cores. However, recovery was poor and we made the decision to continue with the APC system. Formation temperature measurements were collected with the APCT-3 tool on Cores U1621A-4H, 7H, and 10H. Headspace gas C1/C2 ratios were monitored for safety and were in the normal range.

Cores U1621A-1H to 7H were run through the whole-round physical properties track systems, and Cores U1620D-66X to 73X and U1621A-1H to 4H were split and described. The cores described from Hole U1620D predominantly consist of hard, mostly structureless, very rarely laminated silty clay. Authigenic carbonate clasts, pyrite, and small authigenic sulphates were present in several sections of the described interval. The cores described from Hole U1621A predominantly consist of very soft, structureless yellowish brown to gray silty clay. Cores U1621A-1H and 2H in particular were soupy due to drilling disturbance and the high water content of the sediments. Cores U1621A-3H and 4H contained several isolated patches of sandy mud and sand.

Daily science report for 6 July 2024

Location:

  • Hole U1620D (78°16.3332′N, 5°53.6161′E; water depth 1586 m)
  • In transit to proposed Site BED-01A (Site U1621)

Science Update: Core U1620D-73X was retrieved from 608.7 to 616.0 mbsf, the final depth of the hole. Headspace gas C1/C2 ratios were monitored for safety and were in the normal range. Hole U1620D reached a maximum penetration of 616.0 mbsf and recovered 667.89 m of sediment (108% recovery).

In preparation for downhole logging, the pipe was pulled from the hole with the bit positioned at a depth of 71.5 mbsf. The triple combo tool string was rigged up by the Schlumberger Engineer, and it was deployed at 0700 h. Two successful passes (one main pass) of the triple combo reached a depth of 579.5 mbsf, indicating some fill-in at the bottom of the hole. On the main pass, the Schlumberger Engineer noticed a significant overpull and the caliper measurements indicated that a large section of the hole closed in at a rate of about 1 inch/h. The triple combo run was successfully completed at 1245 h, and after careful deliberation the decision was made that the hole conditions would not allow a run of the Formation MicroScanner (FMS)-sonic tool string. The drill string was pulled up, and the bit cleared the seafloor at 1423 h and the rig floor at 1800 h. The rig floor was secured for transit and the vessel switched from dynamic positioning (DP) mode to cruise mode at 1909 h, ending Hole U1620D and Site U1620. The vessel began its passage to Site U1621 (proposed Site BED-01A) at 1930 h and completed 53 nmi of the 138 nmi transit by the end of the day at an average speed of 11.8 kt.

Cores U1620D-70X to 73X were run through the whole-round physical properties track systems, and Cores U1620D-48X to 65X were split and described. The cores predominantly consist of firm dark gray silty clay, transitioning to hard dark gray silty clay in the lower half of the described interval. Several sections contain reddish orange authigenic concretions. Isolated very rare clasts are present in only a few sections.

Daily science report for 5 July 2024

Location: Hole U1620D (78°16.3332′N, 5°53.6161′E; water depth 1586 m)

Science Update: Cores U1620D-64X to 72X were retrieved from 521.3 to 608.7 mbsf. Headspace gas C1/C2 ratios were monitored for safety and were in the normal range.

Cores U1620D-59X to 69X were run through the whole-round physical properties track systems, and Cores U1620D-33X to 47X were split and described. The cores predominantly consist of firm dark gray structureless silty clay with dispersed to common clasts. Several cores have intervals of thin, millimeter-scale variations. Two intervals between 2 and 5 cm thick were identified that consist of tan concretions that were preliminarily identified as authigenic carbonates.

Daily science report for 4 July 2024

Location: Hole U1620D (78°16.3332′N, 5°53.6161′E; water depth 1586 m)

Science Update: Cores U1620D-48X to 63X were retrieved from 376.5 to 521.3 mbsf. Cores U1620D-48X to 53X were advanced by 8 m to allow for gas expansion and full advances resumed at Core U1620D-54X. Headspace gas C1/C2 ratios were monitored for safety, and the ratio was in the normal range. Everyone on board celebrated the Fourth of July and also Hump Day, the halfway point for Expedition 403.

Cores U1620D-41X to 58X were run through the whole-round physical properties track systems, and Cores U1620D-19X to 32X were split and described. The cores predominantly consist of firm dark gray to dark greenish gray silty clay with isolated layers of tan clayey sand. Isolated small (millimeter scale) iron oxides are abundant in some sections throughout the described interval. Clasts (ice-rafted debris [IRD]) are dispersed to common.

Daily science report for 3 July 2024

Location: Hole U1620D (78°16.3332′N, 5°53.6161′E; water depth 1586 m)

Science Update: Cores U1620D-30X to 47X were retrieved from 232.5 to 376.5 mbsf. The cores were advanced by 8 m to allow for gas expansion. Formation temperature measurements were collected with the SET2 tool after Cores U1620D-37X and 43X. Headspace gas C1/C2 ratios were being monitored for safety and the ratio was in the normal range.

Cores U1620D-16X to 40X were run through the whole-round physical properties track systems, and Cores U1620C-16X to 21X and U1620D-1H to 18X were split and described. The cores described from Hole U1620C predominantly consist of silty clay with common to abundant clasts and isolated intervals of sandy mud and isolated authigenic pyrite. The cores described from Hole U1620D predominantly consist of soft dark gray silty clay with intervals of sandy mud, to firm dark gray silty clay beginning in the middle of the described interval. Clasts are mostly dispersed and become more abundant downhole.

Daily science report for 2 July 2024

Location: Hole U1620D (78°16.3332′N, 5°53.6161′E; water depth 1586 m)

Science Update: The vessel arrived at the coordinates of Hole U1620D at 0015 h. After servicing the rig, the bit was positioned and the hole was spudded at 0214 h. Core U1620D-1H recovered a good mudline and 5.98 m of sediment, placing the seafloor depth at 1586 mbsl. Cores U1620D-1H to 29X were retrieved from 0 to 232.5 mbsf. To allow for gas expansion, all XCB cores were advanced by 7 to 8 m. Headspace gas C1/C2 ratios were being monitored for safety. Gas values kept plotting in the anomalous zone, but relying on yesterday’s EPSP assessment, it was deemed safe to proceed.

Cores U1620C-21X and U1620D-1H to 15X were run through the whole-round physical properties track systems. Sections from Cores U1620D-2H to 4H and 6H–7H were split out of order for sedaDNA sampling and, along with Cores U1620C-10H to 15X, were subsequently described. The cores described from Hole U1620C predominantly consist of gray silty clay with isolated intervals of sandy mud with dispersed to common clasts. The cores described from Hole U1620D predominantly consist of soft, structureless clayey silt to sandy mud with dispersed clasts and isolated patches of sand.

Daily science report for 1 July 2024

Location:

  • Hole U1620C (78°16.3566′N, 5°53.8567′E; water depth 1597.1 m)
  • In transit to Hole U1620D

Science Update: The bit was positioned at 1595.3 mbsl and Hole U1620C was spudded next to Hole U1620B at 0033 h. Core U1620C-1H recovered a good mudline and 7.19 m of sediment, placing the seafloor depth at 1597.1 mbsl. Cores U1620C-1H to 21X were retrieved from 0 to 169.9 mbsf, the final depth of the hole. Headspace gas C1/C2 ratios were monitored for safety, and they began plotting on the margin of our safety envelope starting with Core U1620C-16X. All data were sent to shore for further evaluation, and the decision was made to safely proceed while waiting for gas analyses after Cores U1620X-18X to 21X. C1/C2 ratios continued to drop and thus the decision was made to end the hole while waiting for further assessment by the IODP Environmental Protection and Safety Panel (EPSP). Hole U1620C reached a maximum penetration of 169.9 mbsf and recovered 186.89 m of sediment (110% recovery). The drill string was pulled out of the hole to 42.6 m above the seafloor. The bit cleared the seafloor at 2345 h and the vessel was moved 100 m to the southwest along Seismic Line Svyatogor2014_3D_XL222. Before midnight, we received word from the EPSP that it is safe to proceed, which will be taken into account for our operations at Hole U1620D.

Cores U1620B-1H and U1620C-1H to 20X were run through the whole-round physical properties track systems, and Cores U1620A-25X to 31X, U1620B-1H, and U1620C-1H to 9H were split and described. The cores described from Hole U1620A predominantly consist of firm silty clay with dark patches and dispersed to common clasts, and alternating layers of silty clay, sandy mud, and clayey silt in Core U1620A-31X. The short 34 cm long Core U1620B-1H that makes up all of Hole U1620B consists of structureless gray clayey silt. The cores described from Hole U1620C predominantly consist of soft, structureless silty clay to clayey silt with several light gray, greenish, or reddish intervals.