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Sea-level change in the Dutch Wadden Sea
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- Bert L.A. Vermeersen, Aimée B.A. Slangen, Theo Gerkema, Fedor Baart, Kim M. Cohen, Sönke Dangendorf, Matthias Duran-Matute, Thomas Frederikse, Aslak Grinsted, Marc P. Hijma, Svetlana Jevrejeva, Patrick Kiden, Marcel Kleinherenbrink, Erik W. Meijles, Matthew D. Palmer, Roelof Rietbroek, Riccardo E.M. Riva, Elisabeth Schulz, D. Cornelis Slobbe, Matthew J.R. Simpson, Paul Sterlini, Paolo Stocchi, Roderik S.W. van de Wal, Mick van der Wegen
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- Journal:
- Netherlands Journal of Geosciences / Volume 97 / Issue 3 / September 2018
- Published online by Cambridge University Press:
- 11 October 2018, pp. 79-127
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Rising sea levels due to climate change can have severe consequences for coastal populations and ecosystems all around the world. Understanding and projecting sea-level rise is especially important for low-lying countries such as the Netherlands. It is of specific interest for vulnerable ecological and morphodynamic regions, such as the Wadden Sea UNESCO World Heritage region.
Here we provide an overview of sea-level projections for the 21st century for the Wadden Sea region and a condensed review of the scientific data, understanding and uncertainties underpinning the projections. The sea-level projections are formulated in the framework of the geological history of the Wadden Sea region and are based on the regional sea-level projections published in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5). These IPCC AR5 projections are compared against updates derived from more recent literature and evaluated for the Wadden Sea region. The projections are further put into perspective by including interannual variability based on long-term tide-gauge records from observing stations at Den Helder and Delfzijl.
We consider three climate scenarios, following the Representative Concentration Pathways (RCPs), as defined in IPCC AR5: the RCP2.6 scenario assumes that greenhouse gas (GHG) emissions decline after 2020; the RCP4.5 scenario assumes that GHG emissions peak at 2040 and decline thereafter; and the RCP8.5 scenario represents a continued rise of GHG emissions throughout the 21st century. For RCP8.5, we also evaluate several scenarios from recent literature where the mass loss in Antarctica accelerates at rates exceeding those presented in IPCC AR5.
For the Dutch Wadden Sea, the IPCC AR5-based projected sea-level rise is 0.07±0.06m for the RCP4.5 scenario for the period 2018–30 (uncertainties representing 5–95%), with the RCP2.6 and RCP8.5 scenarios projecting 0.01m less and more, respectively. The projected rates of sea-level change in 2030 range between 2.6mma−1 for the 5th percentile of the RCP2.6 scenario to 9.1mma−1 for the 95th percentile of the RCP8.5 scenario. For the period 2018–50, the differences between the scenarios increase, with projected changes of 0.16±0.12m for RCP2.6, 0.19±0.11m for RCP4.5 and 0.23±0.12m for RCP8.5. The accompanying rates of change range between 2.3 and 12.4mma−1 in 2050. The differences between the scenarios amplify for the 2018–2100 period, with projected total changes of 0.41±0.25m for RCP2.6, 0.52±0.27m for RCP4.5 and 0.76±0.36m for RCP8.5. The projections for the RCP8.5 scenario are larger than the high-end projections presented in the 2008 Delta Commission Report (0.74m for 1990–2100) when the differences in time period are considered. The sea-level change rates range from 2.2 to 18.3mma−1 for the year 2100.
We also assess the effect of accelerated ice mass loss on the sea-level projections under the RCP8.5 scenario, as recent literature suggests that there may be a larger contribution from Antarctica than presented in IPCC AR5 (potentially exceeding 1m in 2100). Changes in episodic extreme events, such as storm surges, and periodic (tidal) contributions on (sub-)daily timescales, have not been included in these sea-level projections. However, the potential impacts of these processes on sea-level change rates have been assessed in the report.
Contrast adaptation and excitatory amino acid receptors in cat striate cortex
- J. McLean, L.A. Palmer
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- Journal:
- Visual Neuroscience / Volume 13 / Issue 6 / November 1996
- Published online by Cambridge University Press:
- 02 June 2009, pp. 1069-1087
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We have employed two paradigms to investigate the mechanisms of contrast gain control in cat striate cortex. In the first paradigm, optimal drifting gratings were presented in three consecutive periods. The contrast was near threshold in the first and third periods and accompanied by iontophoretic pulses of glutamate or glutamate receptor (GluR) agonists. The contrast was set to evoke a higher firing rate in the second period. Although both visual and iontophoretic conditions were identical in the first and third periods, responses to glutamate, N-methyl-D-aspartic acid (NMDA), and (1S, 3R)-1-Aminocyclopentane-1, 3-dicarboxylic acid (ACPD) were reduced following the adapting interval. (S)-α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) responses were not reduced. Administration of ionotropic GluR antagonists did not affect adaptation to the high-contrast grating. The metabotropic GluR antagonist (±)-α-Methyl-4-carboxyphenylglycine (MCPG), which acts at presynaptic glutamate autoreceptors, decreased the degree of adaptation exhibited by striate cells. In a second paradigm, contrast response functions (CRFs) were obtained at various adapting contrasts and least-squares fits to a hyperbolic ratio equation generated for each adapting level. Similar to previous reports, DL-2-amino-5-phosphonovaleric acid (APV) reduced the slope of the CRF and increased the responsiveness of the cells but did not affect the semisaturation constant, σ, or the exponent of the CRF, n. Only MCPG significantly altered the distribution of σ and n for 19 cells. The effect on α suggests that this drug can interfere with the cell's ability to shift its operating point to match the adapting contrast. These results suggest the involvement of a presynaptic mechanism for contrast adaptation. The decrease in neuronal responsiveness immediately following the high-contrast period may reflect an additional, postsynaptic effect in which there is a decrease in the NMDA-mediated component of the visual response.
Spatio-temporal receptive-field structure of phasic W cells in the cat retina
- M.H. Rowe, L.A. Palmer
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- Journal:
- Visual Neuroscience / Volume 12 / Issue 1 / January 1995
- Published online by Cambridge University Press:
- 02 June 2009, pp. 117-139
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The spatio-temporal receptive-field structure of 54 phasic W cells in cat retinas has been examined using the reverse-correlation method of Jones and Palmer (1987). Within this sample, 12 cells had on-center, 16 off-center, and 26 on-off receptive fields. Three of the on-center and seven of the on-off cells were directionally selective. Forty percent of the cells in this sample had local receptive fields consisting of two or more distinct subregions. However, no correlation was observed between the number of subregions in the local receptive field and other response properties such as center sign or direction selectivity. In all cases, individual subregions, including those in on-off cells, appear to be produced by a half-wave rectification of the input signal. For 76% of the cells, these local receptive fields were contained within large suppressive fields which could be seen to extend for at least 10 deg in all directions with no apparent spatial structure. The mechanism producing the suppressive field also appears to involve a rectification of the input signal, and has a relatively high spatial resolution. Furthermore, the suppressive field itself is only responsive to moving or flickering stimuli; large, stationary gratings have no effect on the output of the local receptive-field mechanism. Thus, the overall receptive-field organization of these cells is particularly well suited for detecting local motion. The remaining 24% of cells in the sample lacked suppressive fields, and consequently responded well to large moving stimuli, but these cells were otherwise similar in their receptive-field properties to cells with suppressive fields. The significance of these properties is discussed in the context of the projections of phasic W cells to the superior colliculus and accessory optic system.
Plasticity of neuronal response properties in adult cat striate cortex
- J. MCLEAN, L.A. PALMER
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- Journal:
- Visual Neuroscience / Volume 15 / Issue 1 / January 1998
- Published online by Cambridge University Press:
- 01 January 1998, pp. 177-196
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We have utilized an associative conditioning paradigm to induce changes in the receptive field (RF) properties of neurons in the adult cat striate cortex. During conditioning, the presentation of particular visual stimuli were repeatedly paired with the iontophoretic application of either GABA or glutamate to control postsynaptic firing rates. Similar paradigms have been used in kitten visual cortex to alter RF properties (Fregnac et al., 1988, 1992; Greuel et al., 1988; Shulz & Fregnac, 1992). Roughly half of the cells that were subjected to conditioning with stimuli differing in orientation were found to have orientation tuning curves that were significantly altered. In general, the modification in orientation tuning was not accompanied by a shift in preferred orientation, but rather, responsiveness to stimuli at or near the positively reinforced orientation was increased relative to controls, and responsiveness to stimuli at or near the negatively reinforced orientation was decreased relative to controls. A similar proportion of cells that were subjected to conditioning with stimuli differing in spatial phase were found to have spatial-phase tuning curves that were significantly modified. Conditioning stimuli typically differed by 90 deg in spatial phase, but modifications in spatial-phase angle were generally 30–40 deg. An interesting phenomenon we encountered was that during conditioning, cells often developed a modulated response to counterphased grating stimuli presented at the null spatial phase. We present an example of a simple cell for which the shift in preferred spatial phase measured with counterphased grating stimuli was comparable to the shift in spatial phase computed from a one-dimensional Gabor fit of the space-time RF profile. One of ten cells tested had a significant change in direction selectivity following associative conditioning. The specific and predictable modifications of RF properties induced by our associative conditioning procedure demonstrate the ability of mature visual cortical neurons to alter their integrative properties. Our results lend further support to models of synaptic plasticity where temporal correlations between presynaptic and postsynaptic activity levels control the efficiency of transmission at existing synapses, and to the idea that the mature visual cortex is, in some sense, dynamically organized.