Evidence of early deglaciation (18 000 cal a bp) and a postglacial relative sea‐level curve from southern Karmøy,south‐west Norway

Based on six consistent radiocarbon dates from the isolation basins Grødheimsvatnet and Kringlemyr, we estimate a minimum deglaciation age for southern Karmøy, an island in outer Boknafjorden (south‐west Norway), of around 18 000 calibrated years before present (18k cal a bp ). We use microscopic phytoplankton, macrofossils, lithostratigraphic evidence and X‐ray fluorescence data to identify the isolation contacts in the basins, and date them to 17.52–17.18k cal a bp in Grødheimsvatnet [15.57 m above present mean sea level (MSL)] and 16.19–15.80k cal a bp in Kringlemyr (11.99 m above MSL). Combining these data with previous studies, we construct a relative sea‐level (RSL) curve from 18k cal a bp until the present, which is ~3 ka longer than any previous RSL reconstruction from southern Norway. Following deglaciation, southern Karmøy has experienced a net emergence of around 16–19 m, although with significant RSL fluctuations. This includes two RSL minima well below present MSL around ~13.8 and ~10k cal a bp , and two maxima that culminated around 5–7 m above MSL during the Younger Dryas and early to mid‐Holocene, respectively. Considering eustatic sea level and modelled gravitational deformation of the geoid, we estimate a net postglacial isostatic uplift of ~120 m. © 2019 John Wiley & Sons, Ltd     

AUS: Anisotropic undrained shear strength model for clays

A total stress model applicable to clays under undrained conditions is presented. The model involves three strength parameters: the undrained shear strengths in triaxial compression, triaxial extension, and simple shear. The amount of physical anisotropy implied by the model is a function of the relative magnitude of these three strengths assuming a Mises-type plastic potential. Elastoplastic deformation characteristics below failure are accounted for by a hardening law requiring two additional parameters that can be related to the axial strains halfway to failure in triaxial compression and extension. Finally, elasticity is accounted for by Hooke law. The result is a relatively simple model whose parameters can all be inferred directly from a combination of in situ and standard undrained laboratory tests. The model is applied to a problem involving the horizontal loading of a monopile foundation for which full scale tests have been previously conducted. The model shows good agreement with the measured data.     

Climate change during the past 1000 years: a high‐temporal‐resolution multiproxy record from a mire in northern Finland

We present a record of peatland development in relation to climate changes and human activities from the Palomaa mire, a remote site in northern Finland. We used fine‐resolution and continuous sampling to analyse several proxies including pollen (for vegetation on and around the mire), testate amoebae (TA; for mire‐wetness changes), oxygen and carbon isotopes from Sphagnum cellulose (δ¹⁸O and δ¹³C; for humidity and temperature changes), peat‐accumulation rates and peat‐colour changes. In spite of an excellent accumulation model (30 ¹⁴C dates and estimated standard deviation of sample ages <1 year in the most recent part), the potential to determine cause–effect (or lead–lag) relationships between environmental changes and biotic responses is limited by proxy‐specific incorporation processes below the actively growing Sphagnum surface. Nevertheless, what emerges is that mire development was closely related to water‐table changes rather than to summer temperature and that water‐table decreases were associated with increasing peat‐accumulation rates and more abundant mire vegetation. A rapid fen‐to‐bog transition occurred within a few years around AD 1960 when the water table decreased beyond the historical minimum, supporting the notion that mires can rapidly shift into bogs in response to allogenic factors. Copyright © 2012 John Wiley & Sons, Ltd.     

A new approach for reconstructing glacier variability based on lake sediments recording input from more than one glacier

We explore the possibility of building a continuous glacier reconstruction by analyzing the integrated sedimentary response of a large (440 km²) glacierized catchment in western Norway, as recorded in the downstream lake Nerfloen (N61°56’, E6°52’). A multi-proxy numerical analysis demonstrates that it is possible to distinguish a glacier component in the ~ 8000-yr-long record, based on distinct changes in grain size, geochemistry, and magnetic composition. Principal Component Analysis (PCA) reveals a strong common signal in the 15 investigated sedimentary parameters, with the first principal component explaining 77% of the total variability. This signal is interpreted to reflect glacier activity in the upstream catchment, an interpretation that is independently tested through a mineral magnetic provenance analysis of catchment samples. Minimum glacier input is indicated between 6700–5700 cal yr BP, probably reflecting a situation when most glaciers in the catchment had melted away, whereas the highest glacier activity is observed around 600 and 200 cal yr BP. During the local Neoglacial interval (~ 4200 cal yr BP until present), five individual periods of significantly reduced glacier extent are identified at ~ 3400, 3000–2700, 2100–2000, 1700–1500, and ~ 900 cal yr BP.     

Atmospheric mesoscale conditions during the Boothbay meteotsunami: a numerical sensitivity study using a high-resolution mesoscale model

The article aims to test the sensitivity of high-resolution mesoscale atmospheric model to fairly reproduce atmospheric processes that were present during the Boothbay Harbor meteotsunami on 28 October 2008. The simulations were performed by the Weather and Research Forecasting (WRF) model at 1-km horizontal grid spacing by varying initial conditions (ICs) and lateral boundary conditions (LBCs), nesting strategy, simulation lead time and microphysics and convective parameterizations. It seems that the simulations that used higher-resolution IC and LBC were more successful in reproduction of precipitation zone and surface pressure oscillations caused by internal gravity waves observed during the event. The results were very sensitive to the simulation lead time and to the choice of convective parameterization, while the choice of microphysics parameterization and the type of nesting strategy (one-way or two-way) was less important for reproducibility of the event. The success of the WRF model appears limited to very short-range forecasting, most advanced parameterizations, and very high-resolution grid spacing; therefore, the applicability of present atmospheric mesoscale models to future operational meteotsunami warning systems still has a lot of room for improvements.     

Bandlimited implicit Runge–Kutta integration for Astrodynamics

We describe a new method for numerical integration, dubbed bandlimited collocation implicit Runge–Kutta (BLC-IRK), and compare its efficiency in propagating orbits to existing techniques commonly used in Astrodynamics. The BLC-IRK scheme uses generalized Gaussian quadratures for bandlimited functions. This new method allows us to use significantly fewer force function evaluations than explicit Runge–Kutta schemes. In particular, we use a low-fidelity force model for most of the iterations, thus minimizing the number of high-fidelity force model evaluations. We also investigate the dense output capability of the new scheme, quantifying its accuracy for Earth orbits. We demonstrate that this numerical integration technique is faster than explicit methods of Dormand and Prince 5(4) and 8(7), Runge–Kutta–Fehlberg 7(8), and approaches the efficiency of the 8th-order Gauss–Jackson multistep method. We anticipate a significant acceleration of the scheme in a multiprocessor environment.     

ECMWF seasonal forecast system 3 and its prediction of sea surface temperature

The latest operational version of the ECMWF seasonal forecasting system is described. It shows noticeably improved skill for sea surface temperature (SST) prediction compared with previous versions, particularly with respect to El Nino related variability. Substantial skill is shown for lead times up to 1?year, although at this range the spread in the ensemble forecast implies a loss of predictability large enough to account for most of the forecast error variance, suggesting only moderate scope for improving long range El Nino forecasts. At shorter ranges, particularly 3?C6?months, skill is still substantially below the model-estimated predictability limit. SST forecast skill is higher for more recent periods than earlier ones. Analysis shows that although various factors can affect scores in particular periods, the improvement from 1994 onwards seems to be robust, and is most plausibly due to improvements in the observing system made at that time. The improvement in forecast skill is most evident for 3-month forecasts starting in February, where predictions of NINO3.4 SST from 1994 to present have been almost without fault. It is argued that in situations where the impact of model error is small, the value of improved observational data can be seen most clearly. Significant skill is also shown in the equatorial Indian Ocean, although predictive skill in parts of the tropical Atlantic are relatively poor. SST forecast errors can be especially high in the Southern Ocean.     

Ensemble of sea ice initial conditions for interannual climate predictions

Polar climate studies are severely hampered by the sparseness of the sea ice observations. We aim at filling this critical gap by producing two 5-member sea ice historical simulations strongly constrained by ocean and atmosphere observational data and covering the 1958–2006 and 1979–2012 periods. This is the first multi-member sea ice reconstruction covering more than 50 years. The obtained sea ice conditions are in reasonable agreement with the few available observations. These best estimates of sea ice conditions serve subsequently as initial sea ice conditions for a set of 28 3-year-long retrospective climate predictions. We compare it to a set in which the sea ice initial conditions are taken from a single-member sea ice historical simulation constrained by atmosphere observations only. We find an improved skill in predicting the Arctic sea ice area and Arctic near surface temperature but a slightly degraded skill in predicting the Antarctic sea ice area. We also obtain a larger spread between the members for the sea ice variables, thus more representative of the forecast error.     

Effects of elevated CO2 on the reproduction of two calanoid copepods

Some planktonic groups suffer negative effects from ocean acidification (OA), although copepods might be less sensitive. We investigated the effect of predicted CO₂ levels (range 480–750 ppm), on egg production and hatching success of two copepod species, Centropages typicus and Temora longicornis. In these short-term incubations there was no significant effect of high CO₂ on these parameters. Additionally a very high CO₂ treatment, (CO₂ = 9830 ppm), representative of carbon capture and storage scenarios, resulted in a reduction of egg production rate and hatching success of C. typicus, but not T. longicornis. In conclusion, reproduction of C. typicus was more sensitive to acute elevated seawater CO₂ than that of T. longicornis, but neither species was affected by exposure to CO₂ levels predicted for the year 2100. The duration and seasonal timing of exposures to high pCO₂, however, might have a significant effect on the reproduction success of calanoid copepods.