Decoupling of monsoon activity across the northern and southern Indo-Pacific during the Late Glacial

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 176 (2017): 101-105, doi:10.1016/j.quascirev.2017.09.014.Recent studies of stalagmites from the Southern Hemisphere tropics of Indonesia revealed two shifts in monsoon activity not apparent in records from the Northern Hemisphere sectors of the Austral-Asian monsoon system: an interval of enhanced rainfall at ~19 ka, immediately prior to Heinrich Stadial 1, and a sharp increase in precipitation at ~9 ka. Determining whether these events are site-specific or regional is important for understanding the full range of sensitivities of the Austral-Asian monsoon. We present a discontinuous 40 kyr carbon isotope record of stalagmites from two caves in the Kimberley region of the north-central Australian tropics. Heinrich stadials are represented by pronounced negative carbon isotopic anomalies, indicative of enhanced rainfall associated with a southward shift of the intertropical convergence zone and consistent with hydroclimatic changes observed across Asia and the Indo- Pacific. Between 20-8 ka, however, the Kimberley stalagmites, like the Indonesian record, reveal decoupling of monsoon behavior from Southeast Asia, including the early deglacial wet period (which we term the Late Glacial Pluvial) and the abrupt strengthening of early Holocene monsoon rainfall.Funded by grants from the U.S. National Science Foundation Paleo Perspectives on Climate Change program (AGS-1103413 and AGS-1502917 to RFD) and AGS-1602455 (to CCU and RFD), the Center for Global and Regional Environmental Research, and Cornell College (to RFD). CCU acknowledges support from The Investment in Science Fund given primarily by WHOI Trustee and Corporation Members. Support also received from the Kimberley Foundation Australia

EFFECTS OF FISHING ON THE SIZE AND DOMINANCE STRUCTURE OF LINEFISH OF THE CAPE REGION, SOUTH AFRICA

A dataset of linefish catch, effort and fish size distribution records has been assembled from archives to cover three short periods over the 100 years from 1897 to 1998 in four regions of the former Cape Colony, South Africa. Linefish catch and effort have increased several-fold over the period. Aggregate catch per unit effort (cpue) declined by more than 80&#37 from values in the 1890s, but the cpue of several species within that aggregate have declined much more. Analysis of historical mean size and modern length frequency data shows that in seven of 12 species considered, the mean length of fish declined substantially along with the increased fishing pressure. Multivariate analysis of cpue shows that the years 1897–1906 cluster quite close to the years 1927–1931, but a major change by the years 1986–1998, revealing a large change in abundances of linefish between the 1930s and the 1990s, which is also the period when fishing effort increased most. A related dataset was used to calculate the combined distribution of fish sizes of the 12 species in logarithmic size-classes in the same years. The negative slope of that size spectrum indicates the decline in numbers of large size-classes compared with small ones; the more negative the slope, the greater the relative decline in numbers of large fish. Slopes become significantly more negative in the modern period, showing that the modern linefish catch has fewer large fish and relatively more small ones than previously. Changes in linefish assemblages, implied by changes in catch composition, are different in the four regions studied. The cool-temperate upwelling regions differ from the warm-temperate ones, particularly with regard to the influence of the fast-growing, nomadic, pelagic snoek Thyrsites atun. Inclusion of snoek gives the size spectrum of the cool-temperate regions a shallower slope than the warm-temperate ones. A new method of plotting the size spectrum is believed to free the intercept (height) from dependence on the slope and simplifies interpretation of the relative values of height, which reflect overall fish abundance. Dominance curves reflect the distribution of biomass among species. The cool waters of the Western Cape show a trend towards increasing dominance with increased effort, whereas the warm-temperate regions show decreased dominance with increased fishing pressure. These findings have important consequences for fisheries management, because not only are several stocks badly overfished, but the linefish considered are predators at different trophic levels that influence the tropho-dynamic functioning of whole ecosystems.Afr. J. mar. Sci. 26: 161–17

Oxygen and temperature influence the distribution of deepwater Cape hake Merluccius paradoxus in the southern Benguela: a GAM analysis of a 10-year time-series

Generalised additive models (GAMs) were applied to survey data to assess the influence of dissolved oxygen, water temperature and year of sampling upon the presence/absence of small (≤15 cm TL), medium (16–34 cm TL) and large (≥35 cm TL) size classes of deepwater Cape hake Merluccius paradoxus captured off the west coast of South Africa. Data were obtained from surveys using the RV Dr Fridtjof Nansen conducted in 2003 and from 2005 to 2013 during summer (January–February). Among the variables investigated, oxygen was the most important for the small size class (juveniles), with both low and high constraints (two-sided, ‘just right’ option), whereas for the medium and large size classes the oxygen effects were one-sided (avoiding lows). This finding, in combination with other published information, suggests that the Orange Banks is a nursery ground for juvenile M. paradoxus and that the area covered by this nursery ground can vary with the optimal oxygen concentration. The temperature constraint was generally wider and weaker than that for oxygen, being two-sided for the small and medium hake and one-sided (avoiding highs) for the large hake. The medium hake displayed the greatest tolerance to the investigated variables, which resulted in the widest distribution for this size class. Temperature, oxygen and sampling year play an important role in determining the distribution of M. paradoxus, but details of the biology (life cycle) of the species, such as its pelagic–demersal transition and associated movements, are no less important.publishedVersio

Sensitivity of northwest Australian tropical cyclone activity to ITCZ migration since 500 CE

Tropical cyclones (TCs) regularly form in association with the intertropical convergence zone (ITCZ), and thus, its positioning has implications for global TC activity. While the poleward extent of the ITCZ has varied markedly over past centuries, the sensitivity with which TCs responded remains poorly understood from the proxy record, particularly in the Southern Hemisphere. Here, we present a high-resolution, composite stalagmite record of ITCZ migrations over tropical Australia for the past 1500 years. When integrated with a TC reconstruction from the Australian subtropics, this time series, along with downscaled climate model simulations, provides an unprecedented examination of the dependence of subtropical TC activity on meridional shifts in the ITCZ. TCs tracked the ITCZ at multidecadal to centennial scales, with a more southward position enhancing TC-derived rainfall in the subtropics. TCs may play an increasingly important role in Western Australia’s moisture budgets as subtropical aridity increases due to anthropogenic warming

Ecological indicators to capture the effects of fishing on biodiversityand conservation status of marine ecosystems

IndiSeas (“Indicators for the Seas”) is a collaborative international working group that was established in2005 to evaluate the status of exploited marine ecosystems using a suite of indicators in a comparative framework. An initial shortlist of seven ecological indicators was selected to quantify the effects of fishing on the broader ecosystem using several criteria (i.e., ecological meaning, sensitivity to fishing, data avail-ability, management objectives and public awareness). The suite comprised: (i) the inverse coefficient of variation of total biomass of surveyed species, (ii) mean fish length in the surveyed community, (iii)mean maximum life span of surveyed fish species, (iv) proportion of predatory fish in the surveyed community, (v) proportion of under and moderately exploited stocks, (vi) total biomass of surveyed species,and (vii) mean trophic level of the landed catch. In line with the Nagoya Strategic Plan of the Convention on Biological Diversity (2011–2020), we extended this suite to emphasize the broader biodiversity and conservation risks in exploited marine ecosystems. We selected a subset of indicators from a list of empirically based candidate biodiversity indicators initially established based on ecological significance to complement the original IndiSeas indicators. The additional selected indicators were: (viii) mean intrinsic vulnerability index of the fish landed catch, (ix) proportion of non-declining exploited species in the surveyed community, (x) catch-based marine trophic index, and (xi) mean trophic level of the surveyed community. Despite the lack of data in some ecosystems, we also selected (xii) mean trophic level of the modelled community, and (xiii) proportion of discards in the fishery as extra indicators. These additional indicators were examined, along with the initial set of IndiSeas ecological indicators, to evaluate whether adding new biodiversity indicators provided useful additional information to refine our under-standing of the status evaluation of 29 exploited marine ecosystems. We used state and trend analyses,and we performed correlation, redundancy and multivariate tests. Existing developments in ecosystem-based fisheries management have largely focused on exploited species. Our study, using mostly fisheries independent survey-based indicators, highlights that biodiversity and conservation-based indicators are complementary to ecological indicators of fishing pressure. Thus, they should be used to provide additional information to evaluate the overall impact of fishing on exploited marine ecosystems

Implications of the HIV testing protocol for refusal bias in seroprevalence surveys

Background: HIV serosurveys have become important sources of HIV prevalence estimates, but these estimates may be biased because of refusals and other forms of non-response. We investigate the effect of the post-test counseling study protocol on bias due to the refusal to be tested. Methods: Data come from a nine-month prospective study of hospital admissions in Addis Ababa during which patients were approached for an HIV test. Patients had the choice between three consent levels: testing and post-test counseling (including the return of HIV test results), testing without post-test counseling, and total refusal. For all patients, information was collected on basic sociodemographic background characteristics as well as admission diagnosis. The three consent levels are used to mimic refusal bias in serosurveys with different post-test counseling study protocols. We first investigate the covariates of consent for testing. Second, we quantify refusal bias in HIV prevalence estimates using Heckman regression models that account for sample selection. Results: Refusal to be tested positively correlates with admission diagnosis (and thus HIV status), but the magnitude of refusal bias in HIV prevalence surveys depends on the study protocol. Bias is larger when post-test counseling and the return of HIV test results is a prerequisite of study participation (compared to a protocol where test results are not returned to study participants, or, where there is an explicit provision for respondents to forego post-test counseling). We also find that consent for testing increased following the introduction of antiretroviral therapy in Ethiopia. Other covariates of refusal are age (non-linear effect), gender (higher refusal rates in men), marital status (lowest refusal rates in singles), educational status (refusal rate increases with educational attainment), and counselor. Conclusion: The protocol for post-test counseling and the return of HIV test results to study participants is an important consideration in HIV prevalence surveys that wish to minimize refusal bias. The availability of ART is likely to reduce refusal rates