Mark T. Gibbs

Permian phytogeographic patterns and climate data/model comparisons

The most recent global “icehouse‐hothouse” climate transition in earth history began during the Permian. Warmer polar conditions, relative to today, then persisted through the Mesozoic and into the Cenozoic. We focus here on two Permian stages, the Sakmarian (285–280 Ma) and the Wordian (267–264 Ma; also known as the Kazanian), integrating floral with lithological data to determine their climates globally. These stages postdate the Permo‐Carboniferous glaciation but retain a moderately steep equator‐to‐pole gradient, judging by the level of floral and faunal differentiation. Floral data provide a particularly useful means of interpreting terrestrial paleoclimates, often revealing information about climate gradations between “dry” and “wet” end‐member lithological indicators such as evaporites and coals. We applied multivariate statistical analyses to the Permian floral data to calibrate the nature of floral and geographical transitions as an aid to climate interpretation. We then classified Sakmarian and Wordian terrestrial environments in a series of regional biomes (“climate zones”) by integrating information on leaf morphologies and phytogeography with patterns of eolian sand, evaporite, and coal distributions. The data‐derived biomes are compared here with modeled biomes resulting from new Sakmarian and Wordian climate model simulations for a range of CO2 levels (one, four, and eight times the present levels), presented in our companion article. We provide a detailed grid cell comparison of the biome data and model results by geographic region, introducing a more rigorous approach to global paleoclimate studies. The simulations with four times the present CO2 levels (4×CO2) match the observations better than the simulations with 1×CO2, and, at least in some areas, the simulations with 8×CO2 match slightly better than those for 4×CO2. Overall, the 4×CO2 and 8×CO2 biome simulations match the data reasonably well in the equatorial and midlatitudes as well as the northern high latitudes. However, even these highest CO2 levels fail to produce the temperate climates in high southern latitudes indicated by the data. The lack of sufficient ocean heat transport into polar latitudes may be one of the factors responsible for this cold bias of the climate model. Another factor could be the treatment of land surface processes and the lack of an interactive vegetation module. We discuss strengths and limitations of the data and model approaches and indicate future research directions.

Simulations of Permian Climate and Comparisons with Climate‐Sensitive Sediments

We use a climate model to simulate two intervals of Permian climate: the Sakmarian (ca. 280 Ma), at the end of the major Permo‐Carboniferous glaciation, and the Wordian (ca. 265 Ma). We explore the climate sensitivity to various levels of atmospheric CO2 concentration and to changes in geography and topography between the two periods. The model simulates large seasonality and high aridity in the continental interiors of both hemispheres for both periods. The northern summer monsoon weakens and the southern monsoon strengthens between the Sakmarian and the Wordian, owing to changes in geography and topography. The northern middle and high latitudes cool in winter, between the Sakmarian and Wordian, associated with northward shift of the continents. This high‐latitude cooling strengthens the winter westerlies and shifts the maximum storm‐track precipitation south. In the Southern Hemisphere, the winter westerlies weaken from the Sakmarian to the Wordian. Starting the simulations with no permanent ice fields (i.e., by assuming that the late Sakmarian postdates deglaciation) and imposing increased levels of atmospheric CO2 four times the present level, we find no tendency for reinitiation of major glaciation. Some permanent snow fields do develop in high southern latitudes, but these are primarily at high elevation. However, the combination of low CO2 levels (such as present‐day levels) and a cold summer orbital configuration produces expanded areas of permanent snow. The results are based on statistics derived from the final 5 yr of 20‐yr simulations. Paleoenvironmental indicators such as coal, evaporite, phosphate, and eolian sand deposits agree qualitatively with the simulated climate. The extreme cold simulated in high latitudes is inconsistent with estimates of high‐latitude conditions. Either the interpretation of observations is incorrect, the model is incorrect, or both; a possible model deficiency that leads to cold conditions in high latitudes is the relatively weak ocean‐heat transport simulated by the heat diffusion parameterization of the upper ocean model.

Permian climates: Evaluating model predictions using global paleobotanical data

The most recent global icehouse‐hothouse climate transition in Earth history occurred in the Permian. Warmer polar conditions relative to today existed from the middle Permian through the Mesozoic and into the Cenozoic. We focus here on one particularly well-correlated middle Permian stage that postdated the deglaciation, the Wordian (267‐264 Ma), integrating floral and lithological data to determine Wordian climates globally. Paleobotanical data provide the best means of interpreting terrestrial paleoclimates, often revealing important information in the continuum between “dry” and “wet” end-member lithological indicators such as evaporites and coals. New statistical analyses of Wordian floras worldwide have enabled a greater understanding of original vegetation patterns and prevailing climate conditions. The derived climate interpretations are compared with new Wordian atmospheric general circulation model simulations. The model matches the data well in the tropics and northern high latitudes, but predicts colder conditions in southern high latitudes. We discuss possible reasons for this discrepancy.

Aspects of the structure and variability of the low‐salinity‐layer in Doubtful Sound, a New Zealand fiord

Abstract The concurrent actions of fresh water input from the Manapouri power station and the extreme precipitation in the catchment of Doubtful Sound, south‐western New Zealand, results in the maintenance of a surface low‐salinity‐layer (LSL). Although the role of the LSL in controlling subtidal and inter‐tidal assemblages in Doubtful Sound has been documented, little is presently known about the characteristics of the LSL itself. The work presented here aims to elucidate particular aspects of the structure and variability of this ecologically important feature. Synoptic hydrographic data collected during the Doubtful Sound Monitoring Program (DSMP) shows that the LSL is robust and maintained throughout all seasons. Furthermore, hourly salinity and temperature data acquired from four sites within Doubtful Sound show that the major source of variability in the LSL lies in the weather bands although the surface temperatures also exhibited a seasonal component. Time‐series analyses of these data revealed that large perturbations in the LSL were associated with the combined actions of the local wind stress and precipitation. In addition, analysis of data from moored quantum PAR (photosynthetically active radiation) sensors revealed the important influence of the LSL on the subsurface light field.

Baroclinic Response of Sydney Shelf Waters to Local Wind and Deep Ocean Forcing

A study of the forcing processes responsible for upwelling events in the coastal ocean of Sydney, Australia, has been performed using data collected over the summer of 1994 from a shore-normal-aligned mooring array and a numerical model. Analyses of the data show that vertical displacements of fluid in the nearshore zone responded principally to the local wind stress during the experimental period. However, intrusions of mesoscale East Australian Current features are shown to significantly influence the vertical structure of the water column over the middle and outer shelf regions. Numerical simulations are performed to investigate the internal processes occurring during strong steady intrusion events of the East Australian Current onto the Sydney shelf. These simulations suggest that Ekman transport in the bottom boundary layer underlying an intrusion event is not an efficient mechanism for advecting colder water into the nearshore zone on the Sydney shelf. Preconditioning of shelf waters by the East Australian Current and concurrent forcing by local winds is suggested as an efficient process by which upwelling states may be achieved in the Sydney coastal ocean.

Reproductive sources and sinks within a sea urchin, Evechinus chloroticus, population of a New Zealand fjord

We examined population structure of New Zealand sea urchins Evechinus chloroticus across the Doubtful-Thompson Sound complex, a fjord with a large influx of freshwater, a low salin- ity surface layer and a mean estuarine circulation. Measurements of abundance, growth, gonad development and larval settlement were collected at 9 sites. We observed large differences in each of these vital population parameters among sites. The highest growth rates and gamete production occurred at the entrances of the fjord. We used 3 alternative growth models to test whether the spa- tial pattern in growth rates was robust. Variability in growth among sites likely reflected differences in nutritional history, as indicated by the Aristotles lantern index. Size distributions taken 2 yr apart at each of the 9 sites showed that the adult mode was relatively stable in time. As a consequence much of the variance in mean size among sites could be explained by differences in growth rather than in mortality or recruitment. The highest abundance and aggregation of sea urchins occurred at mid-fjord and entrance sites, which coincided with the highest rates of larval settlement and sug- gested limited larval supply elsewhere. The observed spatial patterns in vital rates were used to eval- uate the likely influences of spatial heterogeneity in larval production on larval dispersal patterns within the fjord, based on particle movements within a validated hydrodynamic model. We then tested the sensitivity of these model results to magnitude of wind and rainfall events and duration of larval development. Results from our field observations and modeling studies suggest that the sea urchin population in Doubtful-Thompson Sound is likely composed of distinct areas of reproductive source and sink.

Fishing for More Effective Incentives

In their Report “Can catch shares prevent fisheries collapse?” (19 September 2008, p. [1678][1]), C. Costello et al. present empirical evidence to support the view that providing incentives for fishers by allocating them shares in the catch [individual transferable quotas (ITQs)] can halt, or

Tidal circulation in Tasman and Golden Bays: Implications for river plume behaviour

Abstract An investigation into the tidal residual circulation in the Tasman/Golden Bays system was performed. This investigation involved collecting hydrographic and current meter data, and configuring a numerical circulation model. The model was able to reproduce the gross features of the major tidal flows within the system revealed by the data. The simulated tidal residual circulation conformed to that previously suggested, except along the western side of Tasman Bay where this investigation suggests that residual flows move northwards. The validated model was then used to produce simulations of the fate of the plumes from the major rivers. Salinity field simulations describing different river flow and wind direction/velocity scenarios suggest that the Motueka River plume can cover considerable proportions of western side Tasman Bay, extending into Golden Bay during flood conditions. The embedded sediment transport model was also used to investigate the fate of fine sediments entering the bays. Simulated distribution patterns of fine sediments entering the bays from the four major tributaries were found to be consistent with existing bathymetric and seabed substrate characteristics.

Beyond hydrography: Daily ichthyoplankton variability and short term oceanographic events on the Sydney continental shelf

Abstract Surface ichthyoplankton concentrations along a shore-normal transect across the Sydney continental shelf and upper slope changed between three replicate nights in January and April of 1994. Over 70 families of fish were recorded, which, during January, included: Myctophidae (49% of individuals), Carangidae (14%), Gonostomatidae (11%) and Pomacentridae (8%); and during April included: Gonorhynchidae (43%), Myctophidae (10%), Berycidae (11%) and Serranidae (6%). Multidimensional scaling analysis identified inshore and offshore communities, which nightly moved between the nearshore and mid-shelf stations. During January no distinct near-surface water masses could be identified from the temperature-salinity data, although the shelf waters were under the influence of forcing by the local wind stress and the East Australian Current. Good agreement between the cross-shore transport in the near-surface layer and the temporal variability of the icthyoplankton was nevertheless found. The sampling during April was performed during a period of relatively steady oceanographic conditions, and two water masses were identified from the hydrographic data. Temporal ichthyoplankton variability at any station was correspondingly less during the April period and stable inshore and offshore communities were identified, that shifted with characteristic water masses. The results presented in this paper demonstrate that the large variance often associated with ichthyoplankton distribution within a similar water mass may be interpreted by the dynamics in cross-shelf flows, which has implications for the selection of control sites used when studying environmental impacts of coastal outfalls.

Factors controlling the development of the aquaculture industry in New Zealand: legislative reform and social carrying capacity.

The New Zealand aquaculture sector, consisting of mainly mussel, oyster, and salmon farmers, has been expanding over the last two decades. The increasing demand for water space for marine farming has prompted a process of community consultation and legislative reform resulting in the Aquaculture Reform Act 2004. Despite efforts to develop more effective legislation and improve the application process, marine farmers have often been relatively unsuccessful at gaining the water space that they desire for the expansion of the industry. However, social factors such as landscape and amenity values, recreational and navigational use, and alienation of public space are the most frequently cited reasons for the refusal of marine farm consent applications. An analysis of resource consent decision records from the past decade demonstrates this conclusion that the main factor limiting the further expansion of the aquaculture industry in New Zealand is the social carrying capacity, in the context of a period of legislative transition.