Notes and correspondence

Abstract

This paper is an expansion of the lectures presented by the authors at the Canadian Middle Atmosphere Model (CMAM) summer school, 25–29 August 1997. It attempts to fulfill several goals as did the curriculum for the summer school. Firstly, it has a large tutorial component allowing newcomers a rapid introduction to the field, secondly it surveys the field of stratospheric chemistry, and thirdly it attempts to bring the reader to the forefront of some of the problem areas in stratospheric chemistry. As such, it includes much background information such as the magnitude of rate coefficients, photolysis rates and their calculation and time constants. The intended audience is individuals about to commence study or research in the field of atmospheric chemistry or established atmospheric scientists in other areas wishing to expand their knowledge of this topic.

The basic chemistry of the ozone layer is described with an emphasis on the catalytic cycles and the equilibria between “reservoir” and “active” species. To this end, a compendium of the important aspects of heterogeneous chemistry is also provided. The application of box (0‐dimensional) and more elaborate (1‐, 2‐ and 3‐dimensional) models to compare and validate with measurements is discussed. Also, factors affecting the present and future trends in ozone concentration, both at mid‐latitudes and in the polar region, are presented.     

Age estimation of the Solomon Sea based on heat flow data

Several heat flow measurements were made during the NAT83 cruise in the central part of the Solomon Sea Basin. The average value of 87 mW/m² (2.08 HFU) calculated from these and other data indicates that the age of the Solomon Sea Basin may range from 24 to 44 Ma. This is supported by the water depth, of approximately 4,500 m, versus age relationship. There is a possibility that the Solomon Sea Basin is not a back-arc basin associated with an arc but was formerly a relatively large oceanic plate. The agreement in age from both heat flow and water depth data favors the latter hypothesis.     

Summer sea ice severity in Hudson Strait, 1751–1870

Annual indices of sea ice severity in Hudson Strait, for the period 1751 to 1870, are derived from written historical evidence contained in ships' log-books. These logs were all kept on Hudson's Bay Company ships sailing from London to the Company's trading posts. The log-books are homogeneous in nature and this property facilitates their numerical interpretation. The annual indices are subjected to face validity testing which indicates that they may plausibly be accepted as measures of sea ice severity. The results are examined in relation to the presentday behaviour of sea ice in Hudson Strait and they provide evidence that the summer severity of ice conditions is mainly determined by atmospheric circulation conditions.     

Resolving the discard problem—A case study of the English Nephrops fishery

The phenomenon of discarding was studied using a multidisciplinary approach to allow the integration of biological, social and economic data. The research aimed to evaluate the strength of the case to reduce discarding in a single case study fishery, the English Nephrops fishery; to identify specific objectives for discard reduction; to identify factors that inhibit discard reduction and to determine the best means of achieving those objectives. Changes in trawl structure offered the best solution while having the least impact on fishing opportunities. However, the inadequate level of incentive was identified as the main impediment to discard reduction rather than the lack of technical ability. To implement effective measures to reduce discarding in this fishery, an increased level of incentive is required. Three measures are identified as a means to achieve this.     

Regional setting and structure of the western Solomon Sea

The western Solomon Sea is bounded by the Paleogene collision complex of the Papuan Peninsula to the south, and land masses constructed by Cainozoic volcanism to the north and cast. Oblique collision of two trenches in the western Solomon Sea, and concomitant collision of upper plates, have produced structural complexities that may include the local doubling of crustal thickness, coincident with a strong negative gravity anomaly west of 149°E. Lateral flexing of the subducted plate in the New Britain Trench may have caused flexure of the upper plate; this flexure is expressed in the gravity field, faults, dip-slopes, exposure of basement, and alignment of volcanoes.