The Effect of Macrofauna on Porewater Profiles and Nutrient Fluxes in the Intertidal Zone of the Humber Estuary

Macrofauna, nutrient fluxes, porewater chemistry and sediment characteristics were measured at six intertidal mudflat sites in the Humber Estuary, U.K., during the different seasons. Nereis diversicolor , Macoma balthica and Corophium volutator were found to be the dominant macrofauna. Salinity was the baseline control on macrofauna distribution but this was overprinted by periodic impoverishment due to sediment mobilization. High resolution gel probe porewater samplers provided direct evidence for the impact of burrows on porewater chemistry. The macrofauna modified nutrient fluxes during periods of mud flat stability. Nereis caused a decrease in silicate and phosphate effluxes but enhanced ammonia release and nitrate uptake. Macoma enhanced ammonia and nitrite release. The impact of Corophium was not possible to discern. The Humber is a large, highly dynamic macrotidal estuary in which sediment resuspension has a large impact on porewater profiles, nutrient fluxes and macrofaunal communities. Simple patterns and inter-relationships which are seen in small sheltered estuaries are not observed in the Humber.     

Seismic reflection measurements behind the Hikurangi convergent margin, southern North Island, New Zealand.

Summary. The active Australian-Pacific plate boundary passes through New Zealand. In the north, the Pacific plate subducts beneath the Australian plate with an accretionary wedge forming the eastern continental (Hikurangi) margin of the North Island. The structure of the region behind the Hikurangi margin changes from the extensional back-arc basin under central North Island to a postulated crustal downwarp under the southern North Island. A 100 km long multichannel seismic reflection profile was recorded across the region of crustal downwarp. The data show discontinuous coherent reflectors dipping westwards at the east end of the profile, and east dipping reflectors at the west end, from depths of 9 to 15 s two way time. Simple hand migration of these events indicate that the east dipping reflectors, interpreted as the base of the Australian plate crust, abut against the west dipping reflectors which are interpreted as marking the top of the subducted Pacific plate. Detailed earthquake hypocentre locations in the area show a dipping zone of high seismicity, the top of which coincides closely with the west dipping events, thus supporting this interpretation.     

Seasonal predictability of ENSO teleconnections: the role of the remote ocean response

In this modelling study, the teleconnections of ENSO are studied using an atmospheric general circulation model (AGCM), HadAM3. The influence of sea surface temperature anomalies (SSTAs) remote from the tropical Pacific but teleconnected with ENSO is investigated. Composite cycles of El Niño and La Niña SSTs are created and imposed on HadAM3. These SSTs are imposed in different areas, with climatological SSTs elsewhere, in order to find the influences of SSTs in different regions. It is found that most of the reproducible response to ENSO is forced directly from the tropical Pacific before the peak of the event. However, during the peak and decay of ENSO, remote SSTs become increasingly influential throughout the tropics (at the 98% significance level). This could lead to extended ENSO-related predictability due to the memory of the remote oceans. The Indian Ocean and Maritime Continent SSTs are found to be particularly influential. Indian Ocean SSTAs dampen the teleconnections from the tropical Pacific and force the atmosphere above the tropical Atlantic. More generally, when a tropical SSTA is imposed, atmospheric anomalies are forced locally with anomalies of the opposite sign to the west. Some of the reproducible response to ENSO in the tropical Atlantic is forced, not directly from the tropical Pacific but from the Indian ocean, which in turn is forced by the tropical Pacific. Subsequently, delayed SSTAs in the tropical Atlantic damp the local response and force the atmosphere above the tropical Pacific in the opposite manner.     

Crustal and upper mantle structure of the northwestern North Island, New Zealand, from seismic refraction data

The crustal and upper mantle structure of the northwestern North Island of New Zealand is derived from the results of a seismic refraction experiment; shots were fired at the ends and middle of a 575 km-long line extending from Lake Taupo to Cape Reinga. The principal finding from the experiment is that the crust is 25 ± 2 km thick, and is underlain by what is interpreted to be an upper mantle of seismic velocity 7.6 ± 0.1 km s⁻¹, that increases to 7.9 km s⁻¹ at a depth of about 45 km. Crustal seismic velocities vary between 5.3 and 6.36 km s⁻¹ with an average value of 6.04 km s⁻¹. There are close geophysical and geological similarities between the north-western North Island of New Zealand and the Basin and Range province of the western United States. In particular, the conditions of low upper-mantle seismic velocities, thin crust with respect to surface elevation, and high heat-flow (70–100 mW m⁻²) observed in these two areas can be ascribed to their respective positions behind an active convergent margin for about the past 20 Myr.     

Magnetic anomalies across Campbell Plateau,New Zealand

Magnetic measurements over the Campbell Plateau, New Zealand, show the existence of a linear positive anomaly belt which extends for 900 km along an approximately east-west trend. This anomaly belt is considered to be a continuation of the Stokes Magnetic Anomaly occurring through New Zealand and associated with rocks of the New Zealand Geosyncline. If this is so, a transcurrent fault with a dextral displacement of about 330 km and aligned in a northeast-southwest direction must occur between the eastern end of the Stokes Magnetic Anomaly and the western end of the anomaly belt across Campbell Plateau.     

Paramater regimes for studying isolated eddies

Abstract

The parameter ranges relevant to propagating oceanic eddies are explored with a view to simplifying the equation sets previously used to simulate such eddies. The reduced gravity shallow-water model is used as a starting point. We consider eddies whose width is of the same order as, or somewhat larger than, the Rossby deformation radius. Two model equations emerge from these scalings, both permitting modon solutions and easy numerical integration. Both, too, give fair simulations of the shallow-water model, but disagree in details.

Using another approach, an ad hoc vortex model is used to predict the path of an eddy. This also gives a fair but not perfect simulation of the one-layer results. It appears that the only ideal way to reproduce primitive equation results accurately is to use the primitive equations themselves.     

Wetland Loss Patterns and Inundation-Productivity Relationships Prognosticate Widespread Salt Marsh Loss for Southern New England

Tidal salt marsh is a key defense against, yet is especially vulnerable to, the effects of accelerated sea level rise. To determine whether salt marshes in southern New England will be stable given increasing inundation over the coming decades, we examined current loss patterns, inundation-productivity feedbacks, and sustaining processes. A multi-decadal analysis of salt marsh aerial extent using historic imagery and maps revealed that salt marsh vegetation loss is both widespread and accelerating, with vegetation loss rates over the past four decades summing to 17.3 %. Landward retreat of the marsh edge, widening and headward expansion of tidal channel networks, loss of marsh islands, and the development and enlargement of interior depressions found on the marsh platform contributed to vegetation loss. Inundation due to sea level rise is strongly suggested as a primary driver: vegetation loss rates were significantly negatively correlated with marsh elevation (r ²?=?0.96; p?=?0.0038), with marshes situated below mean high water (MHW) experiencing greater declines than marshes sitting well above MHW. Growth experiments with Spartina alterniflora, the Atlantic salt marsh ecosystem dominant, across a range of elevations and inundation regimes further established that greater inundation decreases belowground biomass production of S. alterniflora and, thus, negatively impacts organic matter accumulation. These results suggest that southern New England salt marshes are already experiencing deterioration and fragmentation in response to sea level rise and may not be stable as tidal flooding increases in the future.