Data Report: carbonate concentrations of Paleogene sediment at Hole 1121B, Campbell Drift

Site 1121 is located southeast of New Zealand on the Campbell Drift (50°53.876´S 176°59.862´E) at a water depth of 4487.90 meters below sea level (mbsl). The site was drilled to recover an expanded sediment sequence from a Neogene contourite drift (Shipboard Scientific Party, 1999). Unexpectedly, the sequence between 32.7 and 132 meters below seafloor (mbsf) is composed of Paleogene siliceous and nannofossil-bearing ooze and chalk (Shipboard Scientific Party, 1999). This finding is intriguing because the location was probably fairly deep (>3800 mbsl) during the Paleogene (Shipboard Scientific Party, 1999), suggesting a carbonate compensation depth (CCD) significantly lower than expected from Cenozoic CCD curves (van Andel, 1975). Therefore, 39 samples of sediment were taken from Hole 1121B to construct a more detailed carbonate record of this interesting lithologic unit

Rock magnetic properties across the Paleocene-Eocene Thermal Maximum in Marlborough, New Zealand

Rock magnetic properties have been investigated across the Paleocene-Eocene Thermal Maximum (PETM) in three uplifted sections of Paleogene marine sedimentary rocks in Marlborough, South Island, New Zealand. The sections are exposed along Mead Stream, Dee Stream and Muzzle Stream and represent a depth transect up a continental margin from an upper slope to an outer shelf. Sampling was focused on rock beds previously examined for their biostratigraphy and stable carbon isotope (d13C) composition, and where a prominent clay-rich interval referred to as Dee Marl marks the initial 80-100 kyr of the PETM. Measured magnetic properties include bulk magnetic susceptibility, hysteresis cycles and isothermal remanent magnetization (IRM) acquisition and back-demagnetization curves. A strong inverse correlation between magnetic susceptibility and bulk carbonate d13C is found across the PETM such that Dee Marl has low d13C and high magnetic susceptibility. At Mead Stream this interval also contains increased saturation-IRM, and thus ferromagnetic content. Rock magnetic behaviour across PETM is best explained by an increase in terrigenous discharge. This inference has been made previously for PETM intervals in New Zealand and elsewhere, although with different proxies. Increased terrigenous discharge probably signifies an acceleration of the hydrological and weathering cycles. Some changes in magnetic phases could also reflect a drop in redox conditions, which could represent higher sedimentation rates, greater input of organic carbon, dysoxic bottom waters, or a combination of all three. A drop in redox conditions has been inferred for other marine sections spanning the PETM

Dynamic simulations of potential methane release from East Siberian continental slope sediments

Sediments deposited along continental margins of the Arctic Ocean presumably host large amounts of methane (CH4) in gas hydrates. Here we apply numerical simulations to assess the potential of gas hydrate dissociation and methane release from the East Siberian slope over the next 100 years. Simulations are based on a hypothesized bottom water warming of 3°C, and an assumed starting distribution of gas hydrate. The simulation results show that gas hydrate dissociation in these sediments is relatively slow, and that CH4 fluxes toward the seafloor are limited by low sediment permeability. The latter is true even when sediment fractures are permitted to form in response to overpressure in pore space. With an initial gas hydrate distribution dictated by present-day pressure and temperature conditions, nominally 0.35 Gt of CH4 are released from the East Siberian slope during the first 100 years of the simulation. However, this CH4 discharge becomes significantly smaller (~0.05 Gt) if glacial sea level changes in the Arctic Ocean are considered. This is because a lower sea level during the last glacial maximum (LGM) must result in depleted gas hydrate abundance within the most sensitive region of the modern gas hydrate stability zone. Even if all released CH4 reached the atmosphere, the amount coming from East Siberian slopes would be trivial compared to present-day atmospheric CH4 inputs from other sources

Expedition 302 summary

The first scientific drilling expedition to the central Arctic Ocean was completed in September 2004. Integrated Ocean Drilling Program Expedition 302, Arctic Coring Expedition (ACEX), recovered sediment cores to 428 meters below seafloor (mbsf) in water depths of ~1300 m, 250 km from the North Pole.Expedition 302's destination was the Lomonosov Ridge, hypothesized to be a sliver of continental crust that broke away from the Eurasian plate at ~56 Ma. As the ridge moved northward and subsided, marine sedimentation occurred and continues to the present, resulting in what was anticipated from seismic data to be a continuous paleoceanographic record. The elevation of the ridge above the surrounding abyssal plains (~3 km) ensured that sediments atop the ridge were free of turbidites. The primary scientific objective of Expedition 302 was to continuously recover this sediment record and to sample the underlying sedimentary bedrock by drilling and coring from a stationary drillship.The biggest challenge during Expedition 302 was maintaining the drillship's location while drilling and coring in 2–4 m thick sea ice that moved at speeds approaching 0.5 kt. Sea-ice cover over the Lomonosov Ridge moves with one of the two major Arctic sea-ice circulation systems, the Transpolar Drift, and responds locally to wind, tides, and currents. Until now, the high Arctic Ocean Basin, known as "mare incognitum" within the scientific community, had never before been deeply cored because of these challenging sea-ice conditions.Initial results reveal that biogenic carbonate is present only in the Holocene–Pleistocene interval. The upper 198 mbsf represents a relatively high sedimentation rate record of the past 18 m.y. and is composed of sediment with ice-rafted debris and dropstones, suggesting that ice-covered conditions extended at least this far back in time. Details of the ice type (e.g., iceberg versus sea ice), timing, and characteristics (e.g., perennial versus seasonal) await further study. A hiatus occurs at 193.13 mbsf, spanning a 25 m.y. interval from the early Miocene to the middle Eocene between ~18 Ma and 43 Ma. The sediment record during the middle Eocene is of dark, organic-rich biosiliceous composition. Isolated pebbles, interpreted as ice-rafted dropstones, are present down to 239 mbsf, well into this middle Eocene interval. Around the lower/middle Eocene boundary an abundance of Azolla spp. occurs, suggesting that a fresh and/or low-salinity surface water setting dominated the region during this time period. Although predrilling predictions based on geophysical data had placed the base of the sediment column at 50 Ma, drilling revealed that the uppermost Paleocene to lowermost Eocene boundary interval, well known as the Paleocene/Eocene Thermal Maximum (PETM), was recovered. During the PETM, the temperature of the Arctic Ocean surface waters exceeded 20°C.Drilling during Expedition 302 also penetrated into the underlying sedimentary bedrock, revealing a shallow-water depositional environment of Late Cretaceous age

Methods

Information assembled in this chapter will help the reader understand the basis for the preliminary conclusions of the Expedition 302 Scientists and will also enable the interested investigator to select samples for further analyses. This information concerns offshore and onshore operations and analyses described in the "Sites M0001–M0004" chapter. Methods used by various investigators for shore-based analyses of Expedition 302 samples will be described in the individual contributions published in the Expedition Research Results and in various professional journals

Sites M0001–M0004

Operations Mobilization of Vidar Viking, Aberdeen, ScotlandThe Vidar Viking came under contract on 22 July 2004, when mobilization began in Aberdeen, Scotland. Mobilization in Aberdeen included two major installations: a moonpool and a full coring/drilling spread. By 26 July, all equipment for the Vidar Viking had arrived, including information technology equipment bound for the Oden. The derrick was load-tested and certified. The Vidar Viking took on a full complement of fuel at Aberdeen.Test Coring Site: Witch Ground, North SeaThe Vidar Viking set sail for Landskrona, Sweden, on 28 July 2004. While the ship was en route, a first test of the drilling equipment was conducted in the Witch Ground area of the North Sea, ~8 h steam from Aberdeen. A test borehole was drilled in 152 m water depth to a depth of 37 meters below seafloor (mbsf) using the British Geological Survey's (BGS's) advanced piston corer (APC) and extended core barrel. Cores were obtained with both systems. The APC recovered >4 m in all runs (maximum = 4.5 m). The Vidar Viking left the test coring site at 1900 h on 30 July and proceeded to Landskrona.Meanwhile, mobilization of the Oden proceeded at Gothenburg, Sweden, which included loading the laboratory equipment. On the evening of 31 July, the Oden set sail for Tromsø, Norway.Mobilization of Vidar Viking, Landskrona, SwedenThe Vidar Viking reached Landskrona on the morning of 1 August 2004. The stern notch, a 100 ton section required by the Vidar Viking when working in ice, and the helideck were installed. The remaining containers were loaded onto the deck, including the core and European Consortium for Ocean Research Drilling Science Operator curation containers sent from Bremen, Germany. Other mobilization work continued until the morning of 3 August, when the Vidar Viking departed for Tromsø.Mobilization of Vidar Viking and Oden, Tromsø, NorwayThe Oden arrived in Tromsø on the evening of 5 August 2004. The Vidar Viking arrived on the morning of 7 August. Two helicopters, required for ice reconnaissance missions, landed on the Oden and were secured.Rendezvous of three Expedition 302 shipsExpedition 302 officially began when the Oden left Tromsø, Norway, at 2350 h on 7 August 2004. The Vidar Viking remained in Tromsø for the next 12 h to wait for dynamic positioning spare parts to arrive.The Oden transited to 81°56'N, 44°59'E to meet the other two ships in the Arctic Coring Expedition (ACEX) fleet for Expedition 302, the Sovetskiy Soyuz and the Vidar Viking, at the edge of the polar ice pack on 10 August. The fleet entered the ice together with the Sovetskiy Soyuz leading, the Oden following, and the Vidar Viking bringing up the rear.Transit to first siteDuring the transit to the operational area, ice reconnaissance and personnel transfer flights began on 12 August 2004. The fleet made unprecedented headway of 8–10 kt in sea ice.The fleet arrived on site at 2350 h on 13 August and began preparations for drilling and operations for maintaining position in sea ice.Preparations for drilling began with clearing ice from the moonpool. Once this was done, a steel skirt was deployed through and below the moonpool to protect the drill string from ice impact below the hull. Once the ice protection skirt was in place, the drill floor and iron roughneck were installed. The drill floor was ready for operations by 0900 h on 15 August.During this time, the fleet's ability to maintain station was tested by positioning the Sovetskiy Soyuz and the Oden upstream of the Vidar Viking. The initial stationkeeping tests were successful, and the Fleet Manager gave approval to start drilling operations at 1100 h on 15 August.Site operationsCores were recovered in five holes (Holes M0002A, M0003A, M0004A, M0004B, and M0004C) (Table T1). Hole M0001A was abandoned after the bottom-hole assembly (BHA) was lost. Logging was attempted in two holes and data were collected in Hole M0004B.Table T2 documents the allocation of time, broken down into (1) waiting for better ice conditions, (2) operational breakdown, and (3) drilling operations.Waiting for better ice conditions was labeled "W." If waiting on ice conditions required pulling pipe and subsequent preparations to begin drilling operations, these times were included in the W category because that time delay was caused by the "waiting for ice" situation. "Breakdown time" is defined as operational time consumed as a result of equipment or mechanical failure. The loss of a BHA, for example, regardless if caused by human error or mechanical failure, necessitated a drill string trip. If the trip time was caused by equipment failure, it was considered as breakdown time "B."Site M0001 (SP 2720 on Line AWI 91090)Site M0001 (shotpoint [SP] 2720 on Line AWI 91090) was reached at 1100 h on 15 August 2004. Later that day during drill string deployment, the high-pressure mud valve on the top drive was damaged. The valve was removed, the rest of the drill string was run, and then the broken valve was replaced. Pipe trips were slowed or stopped intermittently to allow overheated hydraulic fluid in the new drill rig to cool.By 16 August, the drill string was deployed to the seafloor and the first piston corer was deployed at 0600 h. After pumping for 30 min, pressure was not obtained and the piston corer was retrieved without having fired. Damaged seals on the piston corer were replaced. Ice conditions were marginal, and at 0900 h operations were stopped and the drill string was lifted from the seabed. Ice conditions improved by 1400 h, and operations continued. The piston corer was deployed again, and no pressure developed in the drill string. Upon retrieval, the piston corer had not fired. It was suspected that the piston corer had not latched into the BHA. The extended core barrel was then deployed but was not recovered, which indicated that the BHA was lost. At 2000 h, the drill string was tripped to the surface and the BHA and extended core barrel losses were confirmed.Beginning early on 17 August, a new BHA was assembled and lowering of the drill string began. When >800 m was deployed, the high-pressure mud valve on the swivel was damaged during pipe handling. The drill string was tripped to the surface because the operator did not want to risk leaving the drill string hanging in the water column for an unspecified period of time. After completing the pipe trip, the damage was assessed and the Oden's chief engineer was tasked with manufacturing a new valve using materials from a spare pup joint. As an interim solution, a conventional valve assembly was installed, which restricted operations so that no piston core could be deployed.Ice conditions deteriorated between 0900 and 2200 h, and the time was utilized to move the Vidar Viking to a new position (Hole M0002A). Because there were no mud valve spares, the Swedish Polar Research Secretariat began making arrangements for a Swedish Air Force C-130 airdrop of two new valve parts and one conventional valve assembly.Site M0002 (SP 2560 on Line AWI-91090)Based on a strategy developed by the ice management team, the drill string was lowered while drifting onto the location of Site M0002. By 2200 h on 18 August 2004, this strategy put the Vidar Viking within 190 m of the proposed site. The final positioning was done by icebreaking this short distance to Hole M0002A. Once on location at 0820 h, three more drill pipes were added and coring started. Because the mud valve was not yet repaired, the extended core barrel was deployed instead of the APC. A first attempt at coring was unsuccessful, but after adding more pipe and drilling another core run, some core was retrieved. The first core on deck arrived at 1335 h at a water depth of 1209 m. Drilling operations continued throughout the afternoon. The newly fabricated mud valve from the Oden arrived late in the afternoon, and preparations were made for its installation during a wireline trip. The temporary valve was replaced before more drill pipe was added for the next core run. By midnight on 19 August, a depth of 31 mbsf had been reached.Drilling and extended core barrel coring continued until 23 August (Table T1) when the Fleet Manager ordered the drill pipe to be pulled to 40 mbsf because ice conditions had deteriorated. Permission to continue drilling operations was given midday, and operations continued until 2100 h when the ice conditions forced the termination of Hole M0002A at a depth of 271.69 m.The drill string was tripped to the drill deck during the morning of 24 August. After waiting for ice conditions to change in the afternoon, a transit began at 1930 h to a position from which the Vidar Viking could drift onto location while tripping in the drill string.While we waited for improved ice conditions and operations set up for the next site continued, an air gun seismic survey was run from the Oden to tie Site M0002 to the next site (Site M0003).Site M0003 (SP 2521 on Line AWI-91090)The Vidar Viking reached the ice-drift position at 2100 h and awaited ice reconnaissance results. The iron roughneck, which had been removed to repair oil leaks, was installed after repairs; the ice protector skirt was lowered; and the drill floor was prepared. At 2300 h, the BHA and drill collars were run. At 0240 h on 25 August 2004, after 400 m of pipe had been deployed, the housing of the iron roughneck cracked and had to be removed for major repairs. Operations resumed at 1400 h using power tongs. The seafloor was reached at ~2300 h, and at 0110 h on 26 August, the first APC core was recovered from Hole M0003A (Table T1).A second APC core with a shattered liner was recovered. The third APC core became stuck in the BHA. While trying to release the corer, the wireline parted at the mechanical termination, and it was necessary to pull the string. Hole M0003A was terminated at 0440 h.The ice management team conducted ice reconnaissance surveys, reviewed options, and recommended that the fleet move to a location farther west, where a longer-term prediction of relatively good ice could be made. Once the site was selected, the ice team predicted an upstream ice position for the Vidar Viking to start to drift onto the new location. The fleet steamed to the updrift ice position, arriving at 0630 h on 27 August. During this time, wireline termination repair, APC service, and iron roughneck testing and refitting took place.Site M0004 (SP 3006 [Holes M0004A and M0004B] and 3004 [Hole M0004C] on Line AWI-91090)At 0755 h on 27 August 2004 during the pipe trip to the seafloor, the high-pressure mud valve was damaged again. The valve was removed, and the remaining string was run to 1150 m depth while the valve was repaired. At 1800 h, the Vidar Viking was on location (Hole M0004A). Once on station, the repaired mud valve was installed and the drill string was run to the seabed. At 2230 h, drilling operations in Hole M0004A commenced and the hole was advanced by washing ahead to 17 mbsf (Table T1) before a piston corer was deployed.Shortly after midnight on 28 August 2004, the APC became stuck in the BHA but was freed after ~1 h. Once on deck, the plastic liner in the core barrel was found to be shattered and 3.5 m of the core was stuck in the barrel. In light of these problems with the APC—in particular, the risk of junking the hole again—it was decided to switch to extended core barrel coring. Two extended core barrel cores were recovered to a depth of 30.5 mbsf followed by washing to 265 mbsf using the insert bit. This decision to wash ahead was made in order to recover sediment deeper than that recovered in Hole M0002A. By 2240 h, a depth of 265 mbsf was reached.Extended core barrel coring operations continued for the next 3 days (29–31 August), where the hole was advanced at varying rates with good to poor recovery. During this time, the drilling was very slow (e.g., 1 m/h) and recovery in many cores was zero (Cores 302-M0004A-13X through 18X). Different strategies were tried to improve the advance rate. At times, the hole was advanced by washing ahead in an attempt to make faster progress but this strategy was ultimately abandoned after it was found that the washing rate was almost the same as the coring rate. On 31 August from 0200 to 0500 h, for two coring runs in a row no core was recovered. The extended core barrel shoe was switched to a coring shoe for a third attempt at recovery. This coring run cleared a blockage in the bit as evidenced by a large drop in pump pressure. Following this core (with good recovery) and after clearing the blocked bit, core recovery and advancement improved over the next 12 h until basement was reached in Core 302-M0004A-35X. Basement penetration was difficult (8 m penetration in 12 h with low core recovery), and a decision was made at 0900 on 1 September to stop coring at a total depth of 428 mbsf and conduct logging in Hole M0004A.The logging tools were moved to the rig floor, and the tool string (Formation MicroScanner–Accelerator Porosity Sonde–Natural Gamma Ray Spectroscopy Tool–Scintillation Gamma Ray Tool [FMS-APS-NGT-SGT]) and wireline rig-up proceeded simultaneously. The run into hole commenced at 2130 h. This was done at low speed in order to allow the tools to warm up. Communication with the tool was initially established, and it was lowered to the end of the drill pipe. A computer malfunction caused a communication loss to the tools. The problem was corrected by 0200 h. The tool was powered up, and attempts were made to get the tool to pass through the BHA into the open hole. All efforts failed at the same depth (~1366 meters below rig floor [mbrf]); so, while at rest at this depth, the calipers were opened on the FMS to check whether it was free or lodged. The calipers had some movement, which indicated that the tool string was free.The landing ring for the core barrel is the narrowest section of the whole pipe string (95 mm) and lies ~6 m above the bit. All the logging tools had been checked through a landing ring dockside in Aberdeen, but there was no hole calibration ring on board that could be used as a second check. Sequentially, four more logging attempts were made. Each time, it was assumed that the logging tools were too large in diameter and the string diameter was further reduced by removing the larger diameter components. The APS bowspring was removed first, followed by the knuckle joint. Finally, only the narrowest velocity-density string was deployed, which failed to clear the bit at the same depth as the previous runs. After the fifth attempt failed, the logging time allocated had been consumed and attempts to log Hole M0004A ended at 1045 h on 2 September.After the logging gear was cleared away and the drill string was lifted out of the seabed, preparations were made to start a second hole (Hole M0004B) at the site. During preparations, the inner barrel was deployed but did not latch. After an improvised downhole hammer was deployed and worked for 2 h, a short length of core (~10 cm of mudstone), which had been partially blocking the BHA, was recovered.By 2030 h on 2 September, the Vidar Viking was at the new position for the next hole (Hole M0004B). Coring in Hole M0004B started at a depth of 10 mbsf using the extended core barrel because the APC was deemed too risky. After retrieving the first sample, the hole was washed to 20 mbsf for an in situ temperature measurement. The BGS temperature probe was lowered to the base of the hole, pushed into the sediment, and programmed to record the temperature every 5 s. The probe was left to record temperature for 40 min, after which it was retrieved. Plans to wash to a depth of 215 mbsf, core to 230 mbsf, and then wash to 250 mbsf and log were stymied by problems with drilling pressure lines/gauges freezing at –10?C. Because of these problems and the limited time left, the hole was only advanced to a depth of 220 mbsf. Temperature measurements were made at 60 and 100 mbsf.At 0000 h on 4 September, the pipe was pulled to 65 mbsf to prepare for logging. Rigging of the wireline and tool string occurred concurrently, and rig-up of both was completed by 0415 h. The tool string comprised the FMS-Borehole Compensated Sonic (BHC)-NGT-SGT; the choice of tools was such that it coul

Stable isotope and calcareous nannofossil assemblage records for the Cicogna section : toward a detailed template of late Paleocene and early Eocene global carbon cycle and nannoplankton evolution

We present records of stable carbon and oxygen isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages across an 81m thick section of upper Paleocene-lower Eocene marine sedimentary rocks now exposed along Cicogna 5 Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation in a bathyal hemipelagic setting from approximately 57.5 to 52.2 Ma, a multimillion- year time interval characterized by perturbations in the global carbon cycle and changes in calcareous nannofossil assemblages. The bulk carbonate 13C profile for the Cicogna section, once placed on a common time scale, resembles that at sev10 eral other locations across the world, and includes both a long-term drop in 13C, and multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely separated 13C records in marine sequences results from temporal changes in the carbon composition of the exogenic carbon cycle. However, diagenesis has likely modified the 13C record at Cicogna, an interpretation supported by variations in bulk carbonate 15 18O, which do not conform to expectations for a primary signal. The record of CaCO3 content reflects a combination of carbonate dilution and dissolution, as also inferred at other sites. Our detailed documentation and statistical analysis of calcareous nannofossil assemblages show major dierences before, during and after the Paleocene Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit 20 such a distinctive change; instead, these events are sometimes characterized by variations restricted to a limited number of taxa and transient shifts in the relative abundance of primary assemblage components. Both long-lasting and short-lived modifications to calcareous nannofossil assemblages preferentially aected nannoliths or holococcoliths such as Discoaster, Fasciculithus, Rhomboaster/Tribrachiatus, Spenolithus and 25 Zygrhablithus, which underwent distinct variations in abundance as well as permanent evolutionary changes in terms of appearances and disappearances. By contrast, placoliths such as Coccolithus and Toweius, which represent the main component of the assemblages, were characterized by a gradual decline in abundance over time. Comparisons of detailed nannofossil assemblage records at the Cicogna section and at ODP Site 1262 support the idea that variations in relative and absolute abundance, even some minor ones, were globally synchronous. An obvious link is through climate forcing and carbon cycling, although precise linkages to changes in \u3b413C records and 5 oceanographic change will need additional work

Sedimentation and subsidence history of the Lomonosov Ridge

During the first scientific ocean drilling expedition to the Arctic Ocean (Arctic Coring Expedition [ACEX]; Integrated Ocean Drilling Program Expedition 302), four sites were drilled and cored atop the central part of the Lomonosov Ridge in the Arctic Ocean at ~88°N, 140°E (see Fig. F18 in the "Sites M0001–M0004" chapter). The ridge was rifted from the Eurasian continental margin at ~57 Ma (Fig. F1) (Jokat et al., 1992, 1995). Since the rifting event and the concurrent tilting and erosion of this sliver of the outer continental margin, the Lomonosov Ridge subsided while hemipelagic and pelagic sediments were deposited above the angular rifting unconformity (see Fig. F7A in the "Sites M0001–M0004" chapter).The sections recovered from the four sites drilled during Expedition 302 can be correlated using their seismic signature, physical properties (porosity, magnetic susceptibility, resistivity, and P-wave velocity), chemostratigraphy (ammonia content of pore waters), lithostratigraphy, and biostratigraphy. The lithostratigraphy of the composite section combined with biostratigraphy provides an insight into the complex history of deposition, erosion, and preservation of the biogenic fraction. Eventually, the ridge subsided to its present water depth as it drifted from the Eurasian margin. In this chapter, we compare a simple model of subsidence history with the sedimentary record recovered from atop the ridge

Expedition 302 geophysics: integrating past data with new results

In preparation for IODP Expedition 302, Arctic Coring Expedition (ACEX), a site survey database comprising geophysical and geological data from the Lomonosov Ridge was compiled. The accumulated database includes data collected from ice islands, icebreakers, and submarines from 1961 to 2001. In addition, seismic reflection profiles were collected during Expedition 302 that complement the existing seismic reflection data and facilitate integration between the acoustic stratigraphy and the Expedition 302 drill cores. An overview of these data is presented in this chapter.It is well recognized that collecting geophysical data in ice-covered seas, in particular the Arctic Ocean, is a challenging endeavor. This is because much of the Arctic Ocean is continuously covered with ice thicknesses that vary from 1 to 6 m. Over the continental shelves, sea ice can be absent during summer months, but it is present year-round in the central basins. This ice cover is the most dominant feature of the Arctic Ocean environment. It circulates in the ocean basin in two main circulation patterns: the Transpolar Drift and the Beaufort Gyre (see the "Expedition 302 summary" chapter; Rudels et al., 1996).Expedition 302 sites are located within the less severe of these two ice circulation systems, the Transpolar Drift, which primarily moves sea ice from the shelves where it is formed (the Laptev and East Siberian Seas) across the basin and exits through the Fram Strait. During late summer, concentrations of Arctic sea ice can be <100% (10/10 ice cover), making it possible for icebreakers to operate. Average ice concentrations in the central Arctic Ocean during summer months can locally vary from partially open water (6/10) to completely ice covered (10/10). This sea-ice cover can move at speeds up to 0.5 kt.Early Arctic Ocean geophysical exploration was performed from ice-drift stations (Weber and Roots, 1990). However, the tracks from these drifting ice stations were controlled "by the whims of nature" (Jackson et al., 1990), preventing detailed, systematic surveys of predetermined target areas. These ice-drift stations were set up on stable icebergs that were trapped in sea ice and moved generally with the large drift patterns, but locally they were erratic, so preselected locations could not be surveyed. In the late 1980s, single icebreakers began to be used for oceanographic survey work in the Arctic Ocean. Between 1991 and 2001, four scientific icebreaker expeditions to the Lomonosov Ridge took place. These cruises all experienced local sea-ice conditions varying between 8/10 and 10/10. During these expeditions, towed geophysical equipment was occasionally damaged or lost, either because of a rapidly closing wake caused by local ice pressure or because ice had cut the air gun array.Conventionally powered icebreakers reached as far as the North Pole for the first time during the 1991 Expedition (Andersen and Carlsonn, 1992; Fütterer, 1992). Geophysical results from this expedition collected two important reflection profiles, AWI-91090 and AWI-91091, that crossed the Lomonosov Ridge between 87° and 88°N. These profiles imaged a ~450 m thick, well-stratified and apparently undisturbed drape of sediments overlying a prominent acoustic unconformity (Jokat et al., 1992) that spawned the idea to conduct a paleoceanographic drilling expedition to this Ridge.The use of US Navy nuclear submarines for geophysical mapping was implemented through the Science Ice Exercise program (SCICEX) (Newton, 2000). The development of the Seafloor Characterization and Mapping Pods (SCAMP), which hold a Chirp subbottom profiler, swath bathymetric profiler, and side scan sonar, was an essential part of the SCICEX program (Chayes et al., 1996). In 1999, the Lomonosov Ridge geophysical database was augmented with acoustic data acquired during the SCICEX program using the SCAMP system mounted on the US nuclear submarine USS Hawkbill (Edwards and Coakley, 2003)

Continental-scale geographic change across zealandia during paleogene subduction initiation

Data from International Ocean Discovery Program (IODP) Expedition 371 reveal vertical movements of 1-3 km in northern Zealandia during early Cenozoic subduction initiation in the western Pacific Ocean. Lord Howe Rise rose from deep (~1 km) water to sea level and subsided back, with peak uplift at 50 Ma in the north and between 41 and 32 Ma in the south. The New Caledonia Trough subsided 2-3 km between 55 and 45 Ma. We suggest these elevation changes resulted from crust delamination and mantle flow that led to slab formation. We propose a "subduction resurrection" model in which (1) a subduction rupture event activated lithospheric-scale faults across a broad region during less than ~5 m.y., and (2) tectonic forces evolved over a further 4-8 m.y. as subducted slabs grew in size and drove plate-motion change. Such a subduction rupture event may have involved nucleation and lateral propagation of slip-weakening rupture along an interconnected set of preexisting weaknesses adjacent to density anomalies