Changes in wave climate over the northwest European shelf seas during the last 12,000 years

Because of the depth attenuation of wave orbital velocity, wave-induced bed shear stress is much more sensitive to changes in total water depth than tidal-induced bed shear stress. The ratio between wave- and tidal-induced bed shear stress in many shelf sea regions has varied considerably over the recent geological past because of combined eustatic changes in sea level and isostatic adjustment. In order to capture the high-frequency nature of wind events, a two-dimensional spectral wave model is here applied at high temporal resolution to time slices from 12 ka BP to present using paleobathymetries of the NW European shelf seas. By contrasting paleowave climates and bed shear stress distributions with present-day conditions, the model results demonstrate that, in regions of the shelf seas that remained wet continuously over the last 12,000 years, annual root-mean-square (rms) and peak wave heights increased from 12 ka BP to present. This increase in wave height was accompanied by a large reduction in the annual rms wave- induced bed shear stress, primarily caused by a reduction in the magnitude of wave orbital velocity penetrating to the bed for increasing relative sea level. In regions of the shelf seas which remained wet over the last 12,000 years, the annual mean ratio of wave- to (M-2) tidal-induced bed shear stress decreased from 1 (at 12 ka BP) to its present-day value of 0.5. Therefore compared to present- day conditions, waves had a more important contribution to large-scale sediment transport processes in the Celtic Sea and the northwestern North Sea at 12 ka BP

Modeling Antarctic tides in response to ice shelf thinning and retreat

Tides play an important role in ice sheet dynamics by modulating ice stream velocity, fracturing, and moving ice shelves and mixing water beneath them. Any changes in ice shelf extent or thickness will alter the tidal dynamics through modification of water column thickness and coastal topography but these will in turn feed back onto the overall ice shelf stability. Here, we show that removal or reduction in extent and/or thickness of the Ross and Ronne-Filchner ice shelves would have a significant impact on the tides around Antarctica. The Ronne-Filchner appears particularly vulnerable, with an increase in M2 amplitude of over 0.5 m beneath much of the ice shelf potentially leading to tidally induced feedbacks on ice shelf/sheet dynamics. These results highlight the importance of understanding tidal feedbacks on ice shelves/streams due to their influence on ice sheet dynamics

Annually resolved North Atlantic marine climate over the last millennium

This is the final version of the article. Available from Nature Publishing Group via the DOI in this record.Owing to the lack of absolutely dated oceanographic information before the modern instrumental period, there is currently significant debate as to the role played by North Atlantic Ocean dynamics in previous climate transitions (for example, Medieval Climate Anomaly-Little Ice Age, MCA-LIA). Here we present analyses of a millennial-length, annually resolved and absolutely dated marine δ(18)O archive. We interpret our record of oxygen isotope ratios from the shells of the long-lived marine bivalve Arctica islandica (δ(18)O-shell), from the North Icelandic shelf, in relation to seawater density variability and demonstrate that solar and volcanic forcing coupled with ocean circulation dynamics are key drivers of climate variability over the last millennium. During the pre-industrial period (AD 1000-1800) variability in the sub-polar North Atlantic leads changes in Northern Hemisphere surface air temperatures at multi-decadal timescales, indicating that North Atlantic Ocean dynamics played an active role in modulating the response of the atmosphere to solar and volcanic forcing.We thank the members of the RV Bjarni Sæmundsson (Cruise No. B05-2006). This work was supported by the NERC-funded ULTRA project (Grant Number NE/H023356/1), NERC-funded CLAM project; (Project No. NE/N001176/1) and EU Millennium Project (Project number 017008). This study is a contribution to the Climate Change Consortium for Wales (C3W). We thank Brian Long (Bangor University) and Dr Julia Becker (Cardiff University) for their technical support, and Dr Manfred Mudelsee for his assistance with the trend analysis. We thank Dr Jessica Tierney and an anonymous reviewer for providing the constructive comments in the reviewing process

Increased rates of large-magnitude explosive eruptions in Japan in the late Neogene and Quaternary

Tephra layers in marine sediment cores from scientific ocean drilling largely record high-magnitude silicic explosive eruptions in the Japan arc for up to the last 20 million years. Analysis of the thickness variation with distance of 180 tephra layers from a global dataset suggests that the majority of the visible tephra layers used in this study are the products of caldera-forming eruptions with magnitude (M) >6, considering their distances at the respective drilling sites to their likely volcanic sources. Frequency of visible tephra layers in cores indicates a marked increase in rates of large magnitude explosive eruptions at ~8 Ma, 6–4 Ma and further increase after ~2 Ma. These changes are attributed to major changes in tectonic plate interactions. Lower rates of large magnitude explosive volcanism in the Miocene are related to a strike-slip dominated boundary (and temporary cessation or deceleration of subduction) between the Philippine Sea Plate and southwest Japan, combined with the possibility that much of the arc in northern Japan was submerged beneath sea level partly due to previous tectonic extension of Northern Honshu related to formation of the Sea of Japan. Changes in plate motions and subduction dynamics during the ~8 Ma to present period led to (1) increased arc-normal subduction in southwest Japan (and resumption of arc volcanism) and (2) shift from extension to compression of the upper plate in northeast Japan, leading to uplift, crustal thickening and favourable conditions for accumulation of the large volumes of silicic magma needed for explosive caldera-forming eruptions

8.2 ka event North Sea hydrography determined by bivalve shell stable isotope geochemistry

This is the final version. Available on open access from Nature Research via the DOI in this recordThe abrupt 8.2 ka cold event has been widely described from Greenland and North Atlantic records. However, its expression in shelf seas is poorly documented, and the temporal resolution of most marine records is inadequate to precisely determine the chronology of major events. A robust hydrographical reconstruction can provide an insight on climatic reaction times to perturbations to the Atlantic Meridional Overturning Circulation. Here we present an annually-resolved temperature and water column stratification reconstruction based on stable isotope geochemistry of Arctica islandica shells from the Fladen Ground (northern North Sea) temporally coherent with Greenland ice core records. Our age model is based on a growth increment chronology obtained from four radiometrically-dated shells covering the 8290–8100 cal BP interval. Our results indicate that a sudden sea level rise (SSLR) event-driven column stratification occurred between ages 8320–8220 cal BP. Thirty years later, cold conditions inhibited water column stratification but an eventual incursion of sub-Arctic waters into the North Sea re-established density-driven stratification. The water temperatures reached their minimum of ~3.7 °C 55 years after the SSLR. Intermittently-mixed conditions were later established when the sub-Arctic waters receded.Natural Environment Research Council (NERC)European Union FP

Reconstruction of Atlantic herring (Clupea harengus) recruitment in the North Sea for the past 455 years based on the δ13C from annual shell increments of the ocean quahog (Arctica islandica)

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordnderstanding the recruitment variability of the Atlantic herring North Sea stock remains a key objective of stock assessment and management. Although many efforts have been undertaken linking climatic and stock dynamic factors to herring recruitment, no major attempt has been made to estimate recruitment levels before the 20th century. Here, we present a novel annually resolved, absolutely dated herring recruitment reconstruction, derived from stable carbon isotope geochemistry (δ13C), from ocean quahog shells from the Fladen Ground (northern North Sea). Our age model is based on a growth increment chronology obtained from fourteen shells. Ten of these were micromilled at annual resolution for δ13C analysis. Our results indicate that the anthropogenically driven relative depletion of 13C, the oceanic Suess effect (oSE), became evident in the northern North Sea in the 1850s. We calculated a regression line between the oSE‐detrended δ13C results (δ13CṠ) and diatom abundance in the North Sea, the regression being mediated by the effect of phytoplankton on the δ13C of the ambient dissolved inorganic carbon. We used this regression to build an equation mediated by a nutritional link to reconstruct herring recruitment using δ13CṠ. The reconstruction suggests that there were five extended episodes of low‐recruitment levels before the 20th century. These results are supported by measured recruitment estimates and historical fish catch and export documentation. This work demonstrates that molluscan sclerochronological records can contribute to the investigation of ecological baselines and ecosystem functioning impacted by anthropogenic activity with implications for conservation and stock management.Natural Environment Research Council (NERC)FP7 People: Marie‐Curie Action

Global tidal impacts of large-scale ice-sheet collapses

Tide model output for "Wilmes et al., (2017), Global tidal impacts of large-scale ice-sheet collapses, JGR Oceans" together with the Matlab files needed to read the model binary files Please refer to the publications for details on the run setup. h0.* contains elevation output; M2 elevations can be read in Matlab using [h,th_lim,ph_lim] = h_in(filename,1); where h is tidal elevation (abs(h) gives amplitudes and angle(h) gives phase), th_lim gives latitude limits in degs N and ph_lim longitude limits in degs E u0.* contains tidal transport output; M2 transports can be read in Matlab using [u,v,th_lim,ph_lim] = u_in(filename,1); where u and v are transports in x and y direction (real(u)/hz gives tidal current strength) grid* contains the bathymetry; can be read in Matlab using [ll_lims,hz,mz,iob] = grd_in(filename); where ll_lims gives lon and lat limits, hz is water depth, mz is the land-sea mask (0 is land, 1 is water), and iob are open boundary nodes *.it_m2_k1_00.0kyrBP_ish_no0.1sal_191322_sal4 - CTRL; bathymetry: grid_etssib_1_8_paleo_glob_ice_shelves *.it_m2_k1_00.0kyrBP_ish_5mSLR_vw_no0.1sal_191333_sal4 - 5m SLR; bathymetry: grid_etssib_1_8_paleo_glob_ice_shelves_5mSLR_vw *.it_m2_k1_00.0kyrBP_ish_7mSLR_vw_no0.1sal_191336_sal4 - 7m SLR; bathymetry: grid_etssib_1_8_paleo_glob_ice_shelves_7mSLR_vw *.it_m2_k1_1_8th_00.0kyrBP_12mSLR_vw_7048752_sal4 - 12m SLR; bathymetry: grid_etssib_1_8_paleo_glob_ice_shelves_12mSLR_vw *.it_m2_k1_00.0kyrBP_no_wais_fp_5mSLR_vw_no0.1sal_191326_sal4 - No WAIS; bathymetry: grid_etssib_1_8_glob_no_wais_SLR_fingerprint_5m_EEV_vw *.it_m2_k1_00.0kyrBP_no_gris_fp_7mSLR_vw_no0.1sal_191331_sal4 - No GIS; bathymetry: grid_etssib_1_8_glob_no_gris_SLR_fingerprint_7m_EEV_vw *.it_m2_00.0kyrBP_no_wais_gis_fp_vw_375526_sal4 - No WAIS & No GIS; bathymetry: grid_etssib_1_8_glob_no_wais_gris_SLR_fingerprint_12m_EEV_v

Multidecadal ocean variability and NW European ice sheet surges during the last deglaciation

A multiproxy paleoceanographic record from the Atlantic margin off the British Isles reveals in unprecedented detail discharges of icebergs and meltwater in response to sea surface temperature increases across the last deglaciation. We observe the earliest signal of deglaciation as a moderate elevation of sea surface temperatures that commenced with a weakly developed thermocline and the presence of highly ventilated intermediate waters in the Rockall Trough. This warming pulse triggered a series of multidecadal ice-rafted debris peaks that culminated with a major meltwater discharge at 17,500 years before present related to ice sheet disintegration across the NW European region. The impact of meltwater caused a progressive reduction in deep water ventilation and a sea surface cooling phase that preceded the collapse of the Laurentide Ice Sheet during Heinrich event 1 by 500-1000 years. A similar sequence of rapid ocean-ice sheet interaction across the European continental margin is identified during the Bølling-Allerød to Younger Dryas transition. The strategic location of our sediment core suggests a sensitive and rapid response of ice sheets in NW Europe to transient increases in thermohaline heat transport