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Circumpolar Mapping of Antarctic Coastal Polynyas and Landfast Sea Ice
Sinking of dense water from Antarctic coastal polynyas produces Antarctic Bottom Water (AABW), which is the densest water in the global overturning circulation and is a key player in climate change as a significant sink for heat and carbon dioxide. Very recent studies have suggested that landfast sea ice (fast ice) plays an important role in the formation and variability of the polynyas and possibly AABW. However, they have been limited to regional and case investigations only. This study provides the first coincident circumpolar mapping of Antarctic coastal polynyas and fast ice. The map reveals that most of the polynyas are formed on the western side of fast ice, indicating an important role of fast ice in the polynya formation. Winds diverging from a boundary comprising both coastline and fast ice are the primary determinant of polynya formation. The blocking effect of fast ice on westward sea ice advection by the coastal current would be another key factor. These effects on the variability in sea ice production for 13 major polynyas are evaluated quantitatively. Furthermore, it is demonstrated that a drastic change in fast ice extent, which is particularly vulnerable to climate change, causes dramatic changes in the polynyas and possibly AABW formation that can potentially contribute to further climate change. These results suggest that fast ice and precise polynya processes should be addressed by next-generation models to produce more accurate climate projections. This study provides the boundary and validation data of fast ice and sea ice production for such models.
Journal Article
Ocean Bottom Seismometers Provide Direct Measurements of Pulsed‐Structure and Turbulence of Turbidity Currents Overspilling From a Submarine Channel
Turbidity currents transport vast amounts of sediment, carbon, and heat along submarine channels, yet their overspill onto channel‐levees and abyssal mixing remain poorly constrained due to lack of direct observations. Ocean‐bottom seismometers (OBS) deployed on the Congo Canyon–Channel levees captured the structure and turbulence of overspill during an exceptionally large canyon‐flushing event in 2020. Overspill persisted for 3 weeks and comprised numerous short (20‐min to 2‐hr) pulses focused at outer bends. Spectra during overspill show well‐resolved turbulence inertial subranges, yielding event‐average dissipation rates of 10−6–10−5 m2 s−3, comparable to energetic internal‐tide breaking. Abyssal overspill can therefore be long‐lasting and highly pulsed, providing an episodic but locally important source of deep‐ocean mixing. This new view of levee overspill has important implications for building levees and the interpretation of ancient turbidites. Individual levee deposits may be formed incrementally by many pulses of dilute and fine‐grained flow from a single turbidity current.
Journal Article
Ocean discoveries
\"Imagine a fish without a face, drones exploring the ocean floor, and underwater waterfalls! Readers learn all about these amazing underwater discoveries and many more in these carefully-leveled and engaging books reviewed by Smithsonian experts\"-- Provided by publisher.
Book
Development of a sea-sediment coupled model incorporating ocean bottom heat flux
Previous in-situ observations have suggested that bottom water temperature variations in shelf seas can drive significant ocean bottom heat flux (BHF) by heat conduction. The BHF-driven bottom water temperature variations, however, have been overlooked in ocean general circulation models. In this study, we established a sea-sediment fully coupled model through incorporating the BHF. The coupled model included a sediment temperature module/model, and the BHF was calculated based on the sediment heat content variations. Meanwhile, we applied temporally varying BHF in the calculation of the bottom water temperature, which further determined the sediment temperature. The two-way coupled BHF process presents a more complete and physically reasonable heat budget in the ocean model and a synchronously varying sediment temperature profile. The coupled model was validated using a one-dimensional test case, and then it was applied in a domain covering the Bohai and Yellow Seas. The results suggest that when a strong thermocline exists, the BHF can change the bottom water temperature by more than 1°C because the effects of the BHF are limited to within a shallow bottom layer. However, when the water column is well mixed, the BHF changes the temperature of the entire water column, and the heat transported across the bottom boundary is ventilated to the atmosphere. Thus, the BHF has less effect on water temperature and may directly affect air-sea heat flux. The sea-sediment interactions dampen the amplitude of the bottom water temperature variations, which we propose calling the seabed d ampening ocean h eat content variation mechanism (SDH).
Journal Article
Mysteries of the deep : how seafloor drilling expeditions revolutionized our understanding of earth history
\"This book tells the story of how scientific ocean drilling, a crowning achievement of science and engineering in the 20th century, transformed our understanding of Earth's history\"-- Provided by publisher.
Book
B-meson hadroproduction in the SACOT-m T scheme
Abstract We apply the SACOT-m T general-mass variable flavour number scheme (GM-VFNS) to the inclusive B-meson production in hadronic collisions at next-to-leading order in perturbative Quantum Chromodynamics. In the GM-VFNS approach one matches the fixed-order heavy-quark production cross sections, accurate at low transverse momentum (p T), with the zero-mass cross sections, accurate at high p T. The physics idea of the SACOT-m T scheme is to do this by accounting for the finite momentum transfer required to create a heavy quark-antiquark pair throughout the calculation. We compare our results with the latest LHC data from proton-proton and proton-lead collisions finding a very good agreement within the estimated theoretical uncertainties. We discuss also scheme-related differences and their impact on the scale uncertainties.
Journal Article
Enigmatic Tsunami Waves Amplified by Repetitive Source Events Near Sofugan Volcano, Japan
On 8 October 2023, mysterious tsunamis with a maximum wave height of 60 cm were observed in Izu Islands and southwestern Japan, although only seismic events with body‐wave magnitudes mb 4–5 have been documented to the west of Sofugan volcano. To investigate the source process, we analyze tsunami waveforms recorded by an array network of ocean bottom pressure gauges. Stacked waveforms of pressure gauge records suggest recurrent arrivals of multiple wave trains. Deconvolution of the stacked waveforms by tsunami waveforms from an earlier event revealed over 10 source events that intermittently generated tsunamis for ∼1.5 hr. The temporal history of this sequence corresponds to the origin times of T‐phases estimated by an ocean bottom seismometer and of the seismic swarm, implying a common origin. Larger events later in the sequence occurred at intervals comparable to the tsunami wave period, causing amplification of later phases of the tsunami waves. Plain Language Summary On 8 October 2023, mysterious tsunamis hit Izu Islands and southwestern Japan, reaching up to 60 cm in height, although only small‐to‐moderate seismic events were reported in the region. To resolve how the mysterious tsunami waves were generated, we analyze the waves recorded by a tsunami observation network off the southwestern coast of Japan. We find that the tsunami waves were intermittently produced by repetitive source events for approximately 1.5 hr, and the wave amplification happened because the inter‐event times matched the wave periods. These abnormal submarine events excited significant oceanic acoustic waves, as well as measurable tsunamis, which provides valuable information to further study what took place in the ocean. Key Points On 8 October 2023 (UTC), enigmatic tsunamis up to ∼60 cm were recorded along broad Japanese coasts without large earthquakes Analysis of stacked tsunami waveform data shows >10 events intermittently caused tsunamis for ∼1.5 hr with T‐phase and seismic excitation Larger events later in the sequence occurred with intervals similar to the wave period, amplifying the tsunami waves in the later phase
Journal Article