ALBERT

Description: Community structure is defined as the mathematical statistical distribution of the relative species abundance vector. Consideration of the decomposition equation for species richness, S, evenness, E, and the Shannon estimate of entropy or information, H, plus their respective regressions on the accumulation of the number of individuals, N, in a sample leads to the establishment of three structural types. Each type is defined by the slope, {beta}1H, of the regression H versus lnN and depends on the accumulation rate of species between samples (beta-diversity) in a community. These types are designated as 1) Type 0, where H is constant with the accumulation of lnN denoting equilibrium or stability (Log series is a special case); 2) Type 1, where the slope of H is positive with the accumulation of lnN denoting growth or expansion (Log normal is a special case); and 3) Type -1, where the slope of H is negative with the accumulation of lnN denoting decline, instability or stress. In this study, 72 communities were analyzed from environments ranging from marginal marine to the abyss. Only 10 communities are identified as type -1 with the majority of these at lower bathyal and abyssal depths. At abyssal depths the average {beta}1H is -0.057 and data from fossil communities in the Arctic indicate that this unstable, stressed situation has persisted for at least 50 ka. In the Gulf of Mexico at shelf depths, low values for {beta}1H are registered near the Mississippi delta. In contrast, the open-ocean east of New Zealand has an average {beta}1H of 0.227, the highest recorded. Among marginal marine environments an average {beta}1H of -0.030 was recorded in Long Island Sound before the collapse of that community. In contrast, the Indian River Lagoon, Florida had the highest {beta}1H for a marginal marine environment with an average value of 0.195. No simple invariant pattern between type 0 and type 1 communities is prevalent in any environment. Overall 31 communities are type 0 and 31 are type 1. In marginal marine environments (22 communities) the average value of {beta}1H is 0.092. In the open-ocean (50 communities) the average value of {beta}1H is 0.093. Evidently, for any group to remain highly successful on the average a slightly positive value of {beta}1H is required.

Description: An enigma of deep-sea biodiversity research is that the abyss with its low productivity and densities appears to have a biodiversity similar to that of shallower depths. This conceptualization of similarity is based mainly on per-sample estimates (point diversity, within-habitat, or α-diversity). Here, we use a measure of between-sample within-community diversity (β1H) to examine benthic foraminiferal diversity between 333 stations within 49 communties from New Zealand, the South Atlantic, the Gulf of Mexico, the Norwegian Sea, and the Arctic. The communities are grouped into two depth categories: 200–1500 m and 〉1500 m. β1Hdiversity exhibits no evidence of regional differences. Instead, higher values at shallower depths are observed worldwide. At depths of 〉1500 m the average β1His zero, indicating stasis or no biodiversity gradient. The difference in β1H-diversity explains why, despite species richness often being greater per sample at deeper depths, the total number of species is greater at shallower depths. The greater number of communities and higher rate of evolution resulting in shorter species durations at shallower depths is also consistent with higher β1Hvalues.

Description: The lower bathyal Ocean Drilling Program Hole 1261A was sampled near an upper Quaternary oxygen minimum zone (OMZ). Glauconite, the percentage of the foraminiferal assemblage as benthic specimens and assemblage composition were used to investigate the behaviour of the OMZ. Benthic foraminifera and glauconite were comparable with the upper margin of the modern OMZ off California. The percentage abundances of U. peregrina and C. laevigata were on the Demerara Rise negatively correlated, the proportional abundance of U. peregrina increasing upwards through the section. This reflects variations in proximity to the upper margin of the OMZ. This might reflect either crustal subsidence or long-term shallowing of the OMZ during the earlier late Quaternary. Neither hypothesis can be accepted unequivocally. The purported subsidence can be ascribed to crustal loading by the Amazon and Orinoco deep-sea fans, but this would require that the palaeodepth to the top of the OMZ remains constant across several glacial–interglacial cycles. In contrast, it is difficult to envisage any mechanism that could have caused progressive shallowing of the OMZ across several glacial–interglacial cycles. The epifaunal Planulina wuellerstorfi is related to more oxic waters and enhanced current action. This suggests that intervals with more abundant P. wuellerstorfi were somewhat less dysoxic than those with few. These intervals approximate to those with more abundant C. laevigata. Superimposed on this low-frequency signal is a higher-frequency signal, indicated by a between-sample assemblage turnover index (ATIs) that might prove useful for long-range sequence stratigraphic correlation at bathyal depths.