Maureen Walczak - Academia.edu (original) (raw)

Papers by Maureen Walczak

&lt;p&gt;International Ocean Drilling Program (IODP) Expedition 341 in the Gulf o... more &lt;p&gt;International Ocean Drilling Program (IODP) Expedition 341 in the Gulf of Alaska recovered a 112-meter-long sedimentary record from the continental slope at Site U1419. At this site, an exceptionally expanded late Pleistocene sequence (sedimentation rates &gt;100 cm/kyr) combined with a high-resolution radiocarbon chronology (Walczak et al., 2020), provide an opportunity to study Paleomagnetic Secular Variations (PSV) on centennial to millennial timescales over the past ~43,000 years.&lt;br&gt;Natural and laboratory-induced magnetic remanence were measured on u-channels using the stepwise AF demagnetization procedure. In addition to continuous magnetic susceptibility measurements, hysteresis parameters were obtained on 95 discrete samples, and IRM acquisition curves on 9 discrete samples to obtain additional information on the magnetic mineralogy of the sediment. Due to the influence of lithology, magnetic mineralogy, depositional and post-depositional processes, Site U1419 is not suitable for paleointensity studies. However, with removal of intervals influenced by the environmental signal and/or coring deformation, the high sedimentation rates at this site have helped to preserve a reliable record of inclination. Because of signal to noise issues, inclination as measured after the 20 mT AF demagnetization step provides the most accurate estimate. This is demonstrated by comparing the U1419 inclination to a stack of the shipboard inclination at Site U1418 on a new age model developed from 19 radiocarbon dates on U1418 and 18 magnetic susceptibility-based tie-points to site survey core EW0408-87JC (Praetorius et al., 2015). This independently replicated inclination record verifies centennial to millennial scale variations in the Gulf of Alaska that can now be compared with other northeast Pacific and western North American records to begin deciphering geomagnetic variability and provide a new stratigraphic correlation tool for 15 and 30 cal kyr BP interval in this region.&lt;/p&gt;

Geophysical Journal International, Nov 26, 2021

North America suggest that these sites likely capture regional geomagnetic variability. As such, ... more North America suggest that these sites likely capture regional geomagnetic variability. As such, this new high-resolution and well-dated inclination record, especially robust between 15 to 30 cal kyr BP, offers new geomagnetic insights and a regional correlation tool to explore this generally understudied part of the world.

AGU Fall Meeting Abstracts, Dec 1, 2016

Geological Society of America Abstracts with Programs, 2021

Arctic, Antarctic, and Alpine Research, 2020

Calving events of Petermann Glacier, northwest Greenland, in 2010 and 2012 reduced the length of ... more Calving events of Petermann Glacier, northwest Greenland, in 2010 and 2012 reduced the length of its ice tongue by c. 25 km, allowing exploration of newly uncovered seafloor during the Petermann 2015 Expedition. This article presents the results of foraminiferal analysis and environmental data from thirteen surface sediment samples in northern Nares Strait and Petermann Fjord, including beneath the modern ice tongue. This is the first study of living foraminifera beneath an arctic ice tongue and the first modern foraminiferal data from this area. Modern assemblages were studied to constrain species environmental preferences and to improve paleoenvironmental interpretations of foraminiferal assemblages. Sub-ice tongue assemblages differed greatly from those at all other sites, with very low faunal abundances and being dominated by agglutinated fauna, likely reflecting low food supply under the ice tongue. Fjord fauna were comprised of 80 percent or more calcareous species. Notably, Elphidium clavatum is absent beneath the ice tongue although it is dominant in the fjord. Increasing primary productivity associated with the transition to mobile sea ice, diminishing influence of the Petermann Glacier meltwater with distance from the grounding line, and increased influence of south-flowing currents in Nares Strait are the important controls on the faunal assemblages.

Nature Communications, 2020

The uncertain response of marine terminating outlet glaciers to climate change at time scales bey... more The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow advances typical of the tidewater glacier cycle observed in modern systems. When global sea level rise exceeded the local rate of bank building, the cycle of readvances stopped leading to irreversible retreat. These results support theory that suggests sedime...

Quaternary Science Reviews, 2019

We present new sedimentological and environmental magnetic records spanning 18~3.2-2.2 Ma, during... more We present new sedimentological and environmental magnetic records spanning 18~3.2-2.2 Ma, during the intensification of Northern Hemisphere glaciation, from North Atlantic Integrated Ocean Drilling Program Site U1307 on Eirik Drift. Our new datasets and their high-fidelity age control demonstrate that while inland glaciers-and potentially also at times restricted marine-terminating ice-caps-have likely existed on southern Greenland since at least ~3.2 Ma, persistent and extensive marine-terminating glacial margins were only established in this region at 2.72 Ma, ~300 kyr later than in northeastern and eastern Greenland. Despite a dramatic increase in Greenland-sourced ice-rafted debris deposition on Eirik Drift at this time, contemporaneous changes in the bulk magnetic properties of Site U1307 sediments, and a reduction in sediment accumulation rates, suggest a decrease in the delivery of 2 Greenland-sourced glaciofluvial silt, which we attribute to a shift in depositional regime from bottom-current-dominated to glacial-IRD-dominated between ~2.9-2.7 Ma in response to a change in the depth of the flow path of the Western Boundary Undercurrent relative to our study site.

Science Advances, 2020

Deglacial meltwater input to the North Pacific contributed to abrupt Northern Hemisphere climate ... more Deglacial meltwater input to the North Pacific contributed to abrupt Northern Hemisphere climate events.

Quaternary Science Reviews, 2019

Earth and Planetary Science Letters, 2017

High-resolution sedimentary records from two cores from the Gulf of Alaska margin allow developme... more High-resolution sedimentary records from two cores from the Gulf of Alaska margin allow development of a ~17,400 year reconstruction of paleomagnetic secular variation informing on regional and global variability. General agreement between the two records on their independent chronologies confirms that local PSV is recorded, demonstrating that such archives, notwithstanding complexities due to variable sedimentary regimes, deposition rates, and diagenetic conditions, can provide meaningful information on the past changes of the geomagnetic field. Comparisons with other independently-dated sedimentary paleomagnetic records from the greater Northeast Pacific indicate largely coherent inclination records that can be used to produce a regional inclination anomaly stack (NEPSIAS) capturing the common signal over an area spanning >30° longitude and latitude from Alaska through Oregon to Hawaii. Comparison of NEPSIAS with high quality declination records from the northern North Atlantic show significant similarity. Negative (shallow) anomalies in NEPSIAS inclination are associated with eastward NNA declination while positive (steep) anomalies in NEPSIAS inclination are associated with NNA westward declinations. The directional records can be compared to regional geomagnetic intensity over the past ~3000 years in North America and back nearly 9000 years in the Euro/Mediterranean region, suggesting oscillations in the relative strength of the North American flux lobe and Euro/Mediterranean extension of the Siberian flux lobe. This implicates a long-lived organizing structure imposed on the geomagnetic field, perhaps controlled by lower mantle and/or inner core heterogeneities, and supports the potential for stratigraphic correlation of directional PSV as a dating tool throughout the Holocene and perhaps beyond. Comparisons of well-dated paleomagnetic secular variation (PSV) records from the Gulf of Alaska with other independently-dated records (Lake Waiau in Hawaii, Grandfather Lake in Alaska, Fish Lake in Oregon) support the development of a well-defined stack extending back >15,000 cal ybp. This stack illustrates reproducible regional PSV and expands observations of regionally coherent Holocene geomagnetic behavior from Western North America into the Northeastern Pacific region. Covariance of steep inclination in the North Pacific with increased paleointensity in North America, reduced paleointensity in Europe, and westward shifts in declination in the North Atlantic region are consistent with a hypothesis that large scale PSV is driven by variability in the strength of relatively fixed regions of concentrated geomagnetic flux observed over Canada and Northern Eurasia in the modern and historic geomagnetic field. The relationship between Northeast Pacific inclination and North Atlantic declination appears to be consistent back ~12,000 cal ybp; this may indicate the Northern Hemisphere magnetic flux lobes are persistent on millennial scales, with implications for drivers of field morphology as well as the potential of PSV as a stratigraphic tool in the Holocene. Coherence in the inclination behavior of North Pacific records and declination behavior of European records over the Holocene does not support drift of the geomagnetic field as the predominant driver of PSV variability at mid-latitudes on millennial timescales. However, variability in the relative strength of spatially persistent flux lobe patches is a likely driver of 'dipole wobble'.

Proceedings of the National Academy of Sciences of the United States of America, Jan 23, 2015

Erosion, sediment production, and routing on a tectonically active continental margin reflect bot... more Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelera...

Geophysical Journal International, 2015

Proceedings of the IODP, 2014

thrusters and hydrophones were pulled at 0100 h 22 July. Total time spent on Hole U1420A was 189.... more thrusters and hydrophones were pulled at 0100 h 22 July. Total time spent on Hole U1420A was 189.25 h. Lithostratigraphy A lithologic summary of Site U1420 is shown in Figure F5. The total depth of Hole U1420A was 1014.5 m core depth below seafloor (CSF-A). Recovery from 58.2 to 448.5 m CSF-A was <10% but improved deeper than 448.5 m CSF-A, where several cores were collected with recovery between 30% and 94%. Total core recovery for the entire site was 14%. Additionally, numerous drilled rocks and washed clasts were recovered without a supporting matrix lithology. Cores containing mostly drilled rocks and washed clasts include 341-U1420A-10R through 47R, 49R, 52R through 57R, 75R through 79R, and 85R. The limited sediment recovered at Site U1420 contains seven facies. Detailed facies descriptions, information about common marine microfossils, facies occurrence in lithostratigraphic units, and tentative interpretations about depositional environments are summarized in Table T2. The dominant facies (F4f and F4e) are very dark gray (N 3) to dark gray (N 4) clast-rich and clast-poor diamict. Photographs of the most common facies are shown in Figure F6. Based on characteristic facies associations, three lithostratigraphic units were defined (Table T3).

Proceedings of the IODP, 2014

After clearing the seafloor, the vessel was offset 20 m south of Hole U1419B. The bit was then sp... more After clearing the seafloor, the vessel was offset 20 m south of Hole U1419B. The bit was then spaced out and lowered to the first shot depth, and Hole U1419C was spudded at 2100 h on 11 July 2013. An offset water depth of 685.8 mbsl (tide corrected) was used after averaging the tide-corrected water depths from the two previous holes. Hole U1419C was J.M. Jaeger et al. Site U1419 Proc. IODP | Volume 341 3 washed down to 2.0 m DSF, and coring with nonmagnetic core barrels took place for Cores 341-U1419C-2H through 11H (2.0-78.7 m DSF). Partial strokes were recorded on Cores 5H, 7H, 9H, 10H, 14H through 17H, and 19H. The Core Barrel-Drill String Acceleration Tool was run on Cores 2H through 10H as an extension on the APC/XCB core barrel between 2020 h on 11 July and 0450 h on 12 July in order to record drill bit acceleration and vibration signals during drilling. However, the tool malfunctioned downhole, and only ~30 min of reasonable data were recorded. Upon recovery, it was discovered that several supporting screws in the tool were broken, and it seems likely that excessive internal vibration led to small cracks in the sensors, producing intermittent tool response. Cores 11H through 20H (78.7-109.1 m DSF) were recovered using the half APC system. APC recovery was affected by frequently encountered large clasts. Hole U1419C was terminated at 1230 h on 12 July. The hole was displaced with 43 bbl of 10.5 ppg mud, and the drill string was tripped from the hole with the top drive installed. The seafloor was cleared at 1425 h on 12 July, ending Hole U1419C. A total of 19 APC cores were taken over a 107.1 m interval, with 100.37 m recovered (94%). Total time spent on Hole U1419C was 18.8 h. Hole U1419D After clearing the seafloor, the vessel was offset 40 m west of Hole U1419C. The bit was then spaced out and lowered to the first shot depth, and Hole U1419D was spudded at 1720 h on 12 July 2013. An offset water depth of 687.5 mbsl (tide corrected) was used after averaging the tide-corrected water depths from the first two holes at the site. After spudding Hole U1419D, the hole was washed down to 5.5 m DSF and Cores 341-U1419D-2H through 14H were recovered from 5.5 to 80.1 m DSF. Partial strokes were recorded on Cores 6H, 8H, 9H, 11H, 12H, 14H, 17H, 21H, 23H, and 24H. After Core 14H, the half APC coring system was deployed, and coring continued through Core 24H to 114.2 m DSF. The hole was displaced with 40 bbl of 10.5 ppg mud, and the drill string was tripped from the hole with the top drive installed. The seafloor was cleared at 0810 h on 13 July, ending Hole U1419D. A total of 20 APC cores were taken over a 103.7 m interval, with 105.10 m recovered (101%). Three intervals were drilled without coring, which added up to 10.5 m. Total time spent on Hole U1419D was 17.75 h. Hole U1419E After clearing the seafloor, the vessel was offset 20 m north of Hole U1419D. An offset water depth of

Proceedings of the IODP, 2014

Background and objectives Site U1418 is located at 3703 m water depth on a slightly elevated regi... more Background and objectives Site U1418 is located at 3703 m water depth on a slightly elevated region of the proximal Surveyor Fan. It is located between the Aleutian Trench and an abandoned channel, named here the Bering Channel, which also terminated into the trench when active. These channels appear to originate at the base of the slope seaward of the Bering Trough (Fig. F1). This site lies below the westward-flowing Alaska Current, a boundary current within the Alaska Gyre that commonly contains eddies and meanders (Stabeno et al., 2004). Seasonally high productivity is often associated with these eddies (Ladd et al., 2007). The site has likely been supplied with sediment from gravity flows through these adjacent channels, creating a thick (~1 km), seismically stratified deposit (Fig. F2). A large deposit of chaotic seismic facies interpreted as a mass transport deposit (MTD) is found at ~5.8 s two-way traveltime (TWT) (Reece et al., submitted). The top of the MTD forms a reflector that can be mapped to Site U1417, which is dated at ~1 Ma at that site (see "Background and objectives" in the "Site U1417" chapter [Jaeger et al., 2014b]), suggesting that this depocenter may contain an expanded Middle-Late Pleistocene sedimentary sequence. Operations Transit to Site U1418 After a 137 nmi transit from Site U1417 averaging 10.3 kt, the vessel arrived at the second expedition site. The vessel stabilized over Site U1418 at 1455 h (UTC-8 h) on 23 June 2013, and the positioning beacon was deployed at 1515 h. Site U1418 Site U1418 consists of six holes (Table T1), ranging in depth from 17.0 to 948.7 m drillers depth below seafloor (DSF) (Fig. F7). A total of 185 cores were recovered at the site. The interval cored with the advanced piston corer (APC) system was 810.0 m, with 819.08 m recovered (101%). The interval cored with the extended core barrel (XCB) system was 48.5 m, with 22.80 m recovered (47%). The interval cored with the rotary core barrel (RCB) system was 688.7 m, with 495.20 m recovered (72%). The overall recovery for Site U1418 was 86%. Total time spent on Site U1418 was 16.1 days. Hole U1418A Hole U1418A was spudded at 0015 h on 24 June 2013. The mudline core recovered 4.87 m of sediment, and the seafloor was calculated to be 3668.2 m drillers depth below sea level (DSL). Nonmagnetic core barrels and the APC system were used for Cores 341-U1418A-1H through 13H. Temperature measurements were taken with the advanced piston corer temperature tool (APCT-3) shoe on Cores 4H, 7H, 10H, and 13H. APC coring with wireline continued through Core 33H with the half APC coring system using steel core barrels. Partial APC strokes were recorded on Cores 11H, 12H, 13H, 32H, and 33H. Hole U1418A was terminated after Core 33H (209.9 m DSF). The drill string cleared the seafloor 1155 h on 25 June, ending Hole U1418A. A total of 33 piston cores were taken over a 209.9 m interval, with 216.85 m recovered (103%). Total time spent on Hole U1418A was 45.0 h. Hole U1418B After clearing the seafloor, the vessel was offset 20 m east of Hole U1418A. Hole U1418B was spudded at 1355 h on 25 June 2013. The mudline core recovered 7.57 m of sediment, and seafloor was calculated to be 3667.5 m DSL. Nonmagnetic core barrels and the APC system were used for Cores 341-U1418B-1H and 2H. Hole U1418B was terminated after two cores. These cores overlap with a cored interval that was disturbed in the first two cores from Hole U1418A. At the conclusion of coring, the bit was pulled clear of the seafloor, ending Hole U1418B at 1525 h on 25 June. A total of two piston cores were taken over a 17.0 m interval, with 17.08 m recovered (101%). Total time spent on Hole U1418B was 3.5 h. Hole U1418C After clearing the seafloor, the vessel was offset 20 m south of Hole U1418B. Hole U1418C was spudded at 2030 h on 25 June 2013. The mudline core recovered 8.67 m of sediment, and seafloor was calculated to be 3666.0 m DSL. Nonmagnetic core barrels were used and FlexIT orientation was performed for Cores 341-U1418C-1H through 7H. The liner from Core 7H had to be pumped from the core barrel, and the J.M. Jaeger et al. Site U1418 Proc. IODP | Volume 341 3 Facies description Fifteen facies were identified and are outlined in Table T2. The numbering of the facies is based on facies documented for all Expedition 341 sites. Lithofacies include massive mud with lonestones (F1a), massive mud without lonestones (F1b), laminated mud (F1c), silt (F2a), interbedded silt and mud (F2b), very fine to coarse sand (F3a), muddy diamict (F4a), interbedded mud and diamict (F4d), diatom ooze (F5a), biosiliceous ooze (F5b), calcareous/carbonate-bearing mud (F5c), volcanic ash (F6), volcaniclastic mud and sand (F7), rock (F8), and intrastratal contorted mud and diamict (F9). These facies reflect deposition from suspension fall out, sediment gravity flows/largescale mass wasting, ice rafting, variation in organic productivity, and volcanic eruptions. Site U1418 Proc. IODP | Volume 341 109 Table T1. Coring summary, Site U1418. (Continued on next four pages.

Geophysical Journal International, Nov 26, 2021

AGU Fall Meeting Abstracts, Dec 1, 2016

Geological Society of America Abstracts with Programs, 2021

Arctic, Antarctic, and Alpine Research, 2020

Nature Communications, 2020

Quaternary Science Reviews, 2019

Science Advances, 2020

Quaternary Science Reviews, 2019

Earth and Planetary Science Letters, 2017

Proceedings of the National Academy of Sciences of the United States of America, Jan 23, 2015

Geophysical Journal International, 2015

Proceedings of the IODP, 2014