The coral reef crisis: The critical importance of <350 ppm CO2

Temperature-induced mass coral bleaching causing mortality on a wide geographic scale started when atmospheric CO₂ levels exceeded ∼320 ppm. When CO₂ levels reached ∼340 ppm, sporadic but highly destructive mass bleaching occurred in most reefs world-wide, often associated with El Niño events. Recovery was dependent on the vulnerability of individual reef areas and on the reef’s previous history and resilience. At today’s level of ∼387 ppm, allowing a lag-time of 10 years for sea temperatures to respond, most reefs world-wide are committed to an irreversible decline. Mass bleaching will in future become annual, departing from the 4 to 7 years return-time of El Niño events. Bleaching will be exacerbated by the effects of degraded water-quality and increased severe weather events. In addition, the progressive onset of ocean acidification will cause reduction of coral growth and retardation of the growth of high magnesium calcite-secreting coralline algae. If CO₂ levels are allowed to reach 450 ppm (due to occur by 2030-2040 at the current rates), reefs will be in rapid and terminal decline world-wide from multiple synergies arising from mass bleaching, ocean acidification, and other environmental impacts. Damage to shallow reef communities will become extensive with consequent reduction of biodiversity followed by extinctions. Reefs will cease to be large-scale nursery grounds for fish and will cease to have most of their current value to humanity. There will be knock-on effects to ecosystems associated with reefs, and to other pelagic and benthic ecosystems. Should CO₂ levels reach 600 ppm reefs will be eroding geological structures with populations of surviving biota restricted to refuges. Domino effects will follow, affecting many other marine ecosystems. This is likely to have been the path of great mass extinctions of the past, adding to the case that anthropogenic CO₂ emissions could trigger the Earth’s sixth mass extinction.     

Spatial patterns of sub-tidal seagrasses and their tissue nutrients in the Torres Strait,northern Australia: Implications for management

The distribution and nutritional profiles of sub-tidal seagrasses from the Torres Strait were surveyed and mapped across an area of 31,000 km². Benthic sediment composition, water depth, seagrass species type and nutrients were sampled at 168 points selected in a stratified representative pattern. Eleven species of seagrass were present at 56 (33.3%) of the sample points. Halophila spinulosa, Halophila ovalis, Cymodocea serrulata and Syringodium isoetifolium were the most common species and these were nutrient profiled. Sub-tidal seagrass distribution (and associated seagrass nutrient concentrations) was generally confined to northern-central and south-western regions of the survey area (<longitude 142.60), where mean water depth was relatively shallow (approximately 13 m below MSL) and where sediments were comprised primarily muddy sand to gravelly sand. Seagrass nitrogen and starch content, the most important nutrients for marine herbivores, were significantly correlated with species and with the plant component (above or below ground). For all seagrass species, the above-ground component (shoots and leaves) possessed greater nitrogen concentrations than the below-ground component (roots and rhizomes), which possessed greater starch concentrations. S. isoetifolium had the highest total nitrogen concentrations (1.40±0.05% DW). However, it also had higher fibre concentrations (38.2±0.68% DW) relative to the other four species. H. ovalis possessed the highest starch concentrations (2.76±0.12% DW) and highest digestibility (83.24±0.66% DW) as well as the lowest fibre (27.2±0.66% DW). The high relative abundance (found at 55% of the sites that had seagrass) and nutrient quality characteristics of H. ovalis make it an important source of energy to marine herbivores that forage sub-tidally in the Torres Strait. There were two regions in Torres Strait (north-central and south-western) where sub-tidal seagrass meadows were prevalent and of relatively higher nutritional value. This spatial and nutritional information can be used by local agencies to manage and to protect the ecological, economic and cultural values of the sub-tidal seagrass ecosystems and associated fisheries of the Torres Strait.     

Emerging Asias: Introduction

This focus section explores what it means to think geographically about an emergent Asia. The four articles are based on presentations given at the Presidential Plenary session at the 2013 Association of American Geographers annual meeting in Los Angeles. In this Introduction, I briefly examine the temporalities associated with the term emergent and the spatialities evoked by the label Asia, arguing that mainstream conceptions of emergence, as progress into the light, and territorial conceptions of Asia require critical reflection from the perspective of contemporary geographical thought. These issues are taken up in the subsequent articles, examining when is Asia, the U.S. role in constructing representations of Asia, the Japanese origin of global supply chains, and the question of whether Western urban theory suffices to account for urbanization in China.     

Metamorphic zoning and geodynamic evolution of an inverted crustal section (Karakorum margin, N Pakistan), evidence for two metamorphic events

The Karakorum Range comprises a crustal section of marbles and metapelites providing an opportunity to study the extent of high-temperature metamorphic reequilibration in an active orogen. Metamorphism culminated during the Mio-Pliocene, at 6–7 Ma. Peak metamorphic conditions increased from south to north, i.e. from (1) the Upper Anchizone grade (lawsonite, chlorite–smectite) to (2) lower granulite migmatite grade (HT∼800°C) conditions along strike of a 30-km section perpendicular to the structural fabric of the rocks. The metamorphic section can be separated into two domains:

Making local futures tangible—Synthesizing, downscaling, and visualizing climate change scenarios for participatory capacity building

Local in its causes and global in its impacts, climate change still poses an unresolved challenge for scientists, politicians, entrepreneurs, and citizens. Climate change research is largely global in focus, aims at enhanced understanding, and is driven by experts, all of which seem to be insufficient to anchor climate change action in regional and local contexts. We present results from a participatory scenario study conducted in collaboration with the municipality of Delta in SW British Columbia, Canada. This study applies a participatory capacity building approach for climate change action at the local level where the sources of emissions and the mechanisms of adaptation reside and where climate change is meaningful to decision-makers and stakeholders alike. The multi-scale scenario approach consists of synthesizing global climate change scenarios, downscaling them to the regional and local level, and finally visualizing alternative climate scenarios out to 2100 in 3D views of familiar, local places. We critically discuss the scenarios produced and the strengths and weaknesses of the approach applied.