Recent chronologies for tree rings and terrestrial archives using C bomb fallout history

Tree rings representing the period from the mid-1950s up to 2001 were studied as part of an investigation of anthropogenic radionuclide input to terrestrial systems. A live specimen of Pinus sylvestris from the east coast of Ireland was felled, sampled and analysed for comparison with a similar tree felled close to the Atlantic seaboard on the west coast of Ireland. Data for the tree ring sequences were examined relative to the radionuclide content of peat profiles sampled in close proximity to the locations of the studied Pine trees.The data indicate that ¹⁴C concentrations in tree ring sequences from the east and west coasts of Ireland are virtually identical. The sequences show maximum ¹⁴C concentrations (185 and 189 pMC at east and west coast sites, respectively) that correspond closely with published data for atmospheric levels during the height of the nuclear weapons test period (1945-1980). The tree ring count for the specimen from the east coast places the ¹⁴C peak precisely at 1964, the year following the known peak in atmospheric concentrations due to above ground testing of nuclear weapons. However, ¹⁴C data show that simple ring counting of the west coast tree did not provide an accurate chronology. The data demonstrate the importance of applying dendrodating techniques using replicated site chronologies, and the value of the ¹⁴C bomb fallout curve for the construction of recent chronologies. Data show no evidence of enhanced uptake at the east coast that might suggest incorporation of output from the Sellafield nuclear complex or from the release of radioactivity resulting from an accidental fire at the plant in 1957.     

Governing geoengineering research for the Great Barrier Reef

Coral reefs are highly vulnerable to the impacts of rising marine temperatures and marine heatwaves. Mitigating dangerous climate change is essential and urgent, but many reef systems are already suffering on current levels of warming. Geoengineering options are worth exploring to protect the Great Barrier Reef (GBR) from extreme warming conditions, but we contend that they require strong governance and public consultation from the outset. Australian governments are currently funding feasibility testing of three geoengineering proposals for the GBR. Each proposal involves manipulating ocean or atmospheric conditions to lower water temperatures and thereby reduce the threat of mass coral bleaching events. Innovative strategies to protect the GBR and field testing of these is essential, but current laws do not guarantee robust governance for field testing of these technologies. Nor do they provide the foundation for a more coherent national policy on climate intervention technologies more generally. Responsible governance frameworks, including detailed risk assessment and early public consultation, are necessary for geoengineering research to build legitimacy and promote scientific progress.

Key policy insights

• Marine heatwaves pose a serious threat to coral reefs, including Australia’s iconic Great Barrier Reef.

• Australian governments have recognized the threats of warming waters, and are funding research of geoengineering options for the Great Barrier Reef.

• The limited earlier field testing of geoengineering demonstrates the need for specific governance to manage risks, build legitimacy and maintain public support.

• Australia requires a framework to govern geoengineering research and development before deployment of such technologies.

     

A comparison of genetic structure in two low-dispersal crabs from the Wild Coast,South Africa

The Wild Coast in south-eastern South Africa is strongly influenced by the warm, southward-flowing Agulhas Current. This current has a significant impact on dispersal in the coastal biota of the region, and facilitates high levels of connectivity among populations. However, it is not known how the region's high-velocity hydrology affects genetic population structure in endemic estuarine species, populations of which are frequently isolated from the sea. Here, we compared genetic structure in two estuarine crabs of the family Hymenosomatidae. Both are presumed to have low dispersal potential, but they differ in terms of their life histories. Hymenosoma longicrure has abbreviated larval development and can complete its entire life cycle within estuaries, whereas Neorhynchoplax bovis is a direct developer that lacks planktonic larvae. Using DNA sequence data from the mitochondrial COI gene and the intron of the nuclear ANT gene, we found that levels of genetic structure differ considerably between the species. Depending on the genetic marker used, H. longicrure is genetically homogeneous (COI) or displays low levels of genetic structure and minor evidence of recruitment near natal sites (ANT). In contrast, connectivity in N. bovis is much lower, as this species has a unique combination of alleles at each site, indicating that recruitment is mostly local. These results support previous findings suggesting that even a short larval dispersal phase is sufficient to maintain high levels of connectivity and prevent genetic divergence among populations.     

Spatial variation in meristic and morphometric characteristics of sardine Sardinops sagax around the coast of southern Africa

Spatial variability in phenotypic characteristics within a fish population may be used to infer the existence of multiple stocks, and knowledge of the population structure of exploited species is important for their sustainable management. In this study we investigated geographic variability in meristic (vertebral count) and morphometric (body shape) characteristics of sardine Sardinops sagax from three southern African regions: Namibia, the South African west coast, and the South African south coast. There were significant regional differences in vertebral counts, with Namibian fish tending to have more vertebrae than South African fish, but with no difference between sardine off the South African west and south coasts. Body shape was characterised using morphometric landmarks, and shape changes were investigated using geometric morphometrics, with influences on fish shape assessed using multivariate regressions. To remove the effects of allometry, the 22 shape variables (represented by Procrustes coordinates) were regressed against fish size (represented by centroid size). There was a significant allometric effect, which was removed by using the residuals of these regressions in further analyses. A multivariate multiple regression was applied to the 22 size-corrected shape variables and to three covariates: condition factor, stomach fullness and fat stage. The significant influence of these covariates was removed by using the residuals from this regression in a canonical variate analysis, where corrected shape variables were classified in relation to region, year and sex. The Mahalanobis distances from the canonical variate analysis differed significantly for most combinations of classifier variables, with clear separations among the three regions. Sardinops sagax off Namibia had thicker bodies and more contracted tail regions than South African fish, whereas S. sagax off the South African south coast had thinner bodies and smaller heads than those off the west coast. These results support the hypothesis of multiple sardine stocks around southern Africa.     

Labour Market Adjustment in the Time of Krismon: Changes in Employment Structure in Indonesia, 1997–98

This study examines the labour market outcomes of the recent economic crisis ( krismon ) in Indonesia, focusing on the change of employment structure between 1997 and 1998. Indonesia's labour market has been extremely flexible in adjusting itself during the crisis. Labour has moved from "modern" economic sectors to agricultural and "informal" sectors, reflecting the strategy of poor households to cope with the hardship. While the impact of the economic crisis on the majority of male workers has been severe, female labourers have become increasingly involved in several jobs to enable the survival of their families.     

Dynamics of melting beneath a small-scale basaltic system: a U-Th–Ra study from Rangitoto volcano,Auckland volcanic field,New Zealand

The Auckland volcanic field is a Quaternary monogenetic basaltic field of 50 volcanoes. Rangitoto is the most recent of these at ~500 year BP and may mark a change in the behaviour of the field as it is the largest by an order of magnitude and is unusual in that it erupted magmas of alkalic then subalkalic basaltic composition in discrete events separated by ≤50 years. Major and trace element geochemistry together with Sr–Nd and U-Th–Ra isotopes provides the basis for modelling the melting conditions that brought about the eruption of two chemically different lavas with very little spatial or temporal change. Sr–Nd isotopes suggest that the source for both eruptions is similar with a slight degree of heterogeneity. The basalts show high ²³⁰Th-excess compared with comparable continental volcanic fields. We show that the alkalic basalts give evidence for lower degrees of partial melting, higher amounts of residual garnet, a longer melting column and lower melting and upwelling rates compared with the subalkalic basalts. The low upwelling rates (0.1–1.5 cm/year) modelled for both magmas do not suggest a plume or major upwelling in the mantle region beneath Auckland; therefore, we suggest localised convection due to relict movement from the active subduction system situated 400 km to the southeast. A higher porosity for the initial alkalic basalt is based on ²²⁶Ra-excesses, suggesting movement of melt by two different porosities: the initial melt travelling in fast high porosity channels from greater depths preserving a high ²³⁰Th-excess and the subsequent subalkalic magma travelling from a shallower depth through lower porosity diffuse channels preserving a high ²²⁶Ra-excess; this creates a negative array in (²²⁶Ra/²³⁰Th) versus (²³⁰Th/²³⁸U) space previously only seen in mid ocean ridge Basalt data. This mechanism suggests the Auckland volcanic field may operate by the presence of discrete melt batches that are able to move at different depths and speeds giving the field its erratic spatial and temporal pattern of eruptions, a type of behaviour that may have implications for the evolution of other continental volcanic fields worldwide.     

Biophysical models of larval dispersal in the Benguela Current ecosystem

We synthesise and update results from the suite of biophysical, larval-dispersal models developed in the Benguela Current ecosystem. Biophysical models of larval dispersal use outputs of physical hydrodynamic models as inputs to individual-based models in which biological processes acting during the larval life are included. In the Benguela, such models were first applied to simulate the dispersal of anchovy Engraulis encrasicolus and sardine Sardinops sagax ichthyoplankton, and more recently of the early life stages of chokka-squid Loligo reynaudii and Cape hakes Merluccius spp. We identify how the models have helped advance understanding of key processes for these species. We then discuss which aspects of the early life of marine species in the Benguela Current ecosystem are still not well understood and could benefit from new modelling studies.     

A Great Basin-wide dry episode during the first half of the Mystery Interval?

The existence of the Big Dry event from 14.9 to 13.8 ¹⁴C kyrs in the Lake Estancia New Mexico record suggests that the deglacial Mystery Interval (14.5–12.4 ¹⁴C kyrs) has two distinct hydrologic parts in the western USA. During the first, Great Basin Lake Estancia shrank in size and during the second, Great Basin Lake Lahontan reached its largest size. It is tempting to postulate that the transition between these two parts of the Mystery Interval were triggered by the IRD event recorded off Portugal at about 13.8 ¹⁴C kyrs which post dates Heinrich event #1 by about 1.5 kyrs. This twofold division is consistent with the record from Hulu Cave, China, in which the initiation of the weak monsoon event occurs in the middle of the Mystery Interval at 16.1 kyrs (i.e., about 13.8 ¹⁴C kyrs).     

Absence of an effect of freshwater input on the stable isotope and fatty acid signatures of intertidal filter-feeders

Freshwater input is known to have the potential to influence marine pelagic and benthic communities through the export of nutrients, sediments and detritus. The increase in nutrients of riverine origin in coastal environments can enhance primary production in coastal areas, supporting a diverse and rich fauna. However, it is not clear how and to what extent these freshwater inputs influence marine populations. We investigated the potential effects of freshwater input on the diets of intertidal benthic organisms in situ on the east coast of South Africa, analysing their δ¹³C and δ¹⁵N stable isotope and fatty acid content. Specifically, we investigated the dietary regime of three barnacle and one mussel species in relation to their proximity to the mouths of large rivers. Strong dissimilarities among species were recorded with both techniques; however, no significant effect of freshwater input was observed for any of them. There are several possible explanations for these results, including rapid dilution, with fresh water near the river mouth being thoroughly mixed with seawater, resulting in a riverine influence being too weak to be detectable in the signatures of benthic populations. Our results contrast with a previous study conducted in the same area, where it was suggested that demersal organisms relied on freshwater-derived organic matter. Our study, however, showed no freshwater effect either within a few metres or tens of kilometres from the nearest large river mouths, supporting the notion that freshwater input does not play an important role for the benthic intertidal community in the ecosystems studied. Given that freshwater input is likely to diminish in the future, because of increased human abstraction of water, any potential effects of freshwater input on these marine populations are likely to be further reduced.