Showing papers by "Hilary Kennedy published in 2015"

Seagrass meadows as a globally significant carbonate reservoir

Abstract: . There has been growing interest in quantifying the capacity of seagrass ecosystems to act as carbon sinks as a natural way of offsetting anthropogenic carbon emissions to the atmosphere. However, most of the efforts have focused on the particulate organic carbon (POC) stocks and accumulation rates and ignored the particulate inorganic carbon (PIC) fraction, despite important carbonate pools associated with calcifying organisms inhabiting the meadows, such as epiphytes and benthic invertebrates, and despite the relevance that carbonate precipitation and dissolution processes have in the global carbon cycle. This study offers the first assessment of the global PIC stocks in seagrass sediments using a synthesis of published and unpublished data on sediment carbonate concentration from 403 vegetated and 34 adjacent un-vegetated sites. PIC stocks in the top 1 m of sediment ranged between 3 and 1660 Mg PIC ha−1, with an average of 654 ± 24 Mg PIC ha−1, exceeding those of POC reported in previous studies by about a factor of 5. Sedimentary carbonate stocks varied across seagrass communities, with meadows dominated by Halodule, Thalassia or Cymodocea supporting the highest PIC stocks, and tended to decrease polewards at a rate of −8 ± 2 Mg PIC ha−1 per degree of latitude (general linear model, GLM; p

Harnessing the climate mitigation, conservation and poverty alleviation potential of seagrasses: prospects for developing blue carbon initiatives and payment for ecosystem service programmes

Abstract: Seagrass ecosystems provide numerous ecosystem services that support coastal communities around the world. They sustain abundant marine life as well as commercial and artisanal fisheries, and help protect shorelines from coastal erosion. Additionally, seagrass meadows are a globally significant sink for carbon and represent a key ecosystem for combating climate change. However, seagrass habitats are suffering rapid global decline. Despite recognition of the importance of ‘Blue Carbon’, no functioning seagrass restoration or conservation projects supported by carbon finance currently operate, and the policies and frameworks to achieve this have not been developed. Yet, seagrass ecosystems could play a central role in addessing important international research questions regarding the natural mechanisms through which the ocean and the seabed can mitigate climate change, and how ecosystem structure links to service provision. The relative inattention that seagrass ecosystems have received represents both a serious oversight and a major missed opportunity. In this paper we review the prospects of further inclusion of seagrass ecosystems in climate policy frameworks, with a particular focus on carbon storage and sequestration, as well as the potential for developing payment for ecosystem service (PES) schemes that are complementary to carbon management. Prospects for the inclusion of seagrass Blue Carbon in regulatory compliance markets are currently limited; yet despite the risks the voluntary carbon sector offers the most immediately attractive avenue for the development of carbon credits. Given the array of ecosystem services seagrass ecosystems provide the most viable route to combat climate change, ensure seagrass conservation and improve livelihoods may be to complement any carbon payments with seagrass PES schemes based on the provision of additional ecosystem services.

Ikaite Abundance Controlled by Porewater Phosphorus Level: Potential Links to Dust and Productivity

Abstract: Glendonites are pseudomorphs of the mineral ikaite (CaCO3·6H2O) after loss of hydration water and occur in distinctive euhedral crystalline forms, sometimes clustered as rosettes of up to tens of centimeters in diameter. While it is generally accepted that organic-rich environments, methane seeps, and high phosphate levels are important for ikaite formation, glendonite occurrences in ancient sedimentary sequences are widely considered to reflect near-freezing temperatures, even at high latitudes during periods of greenhouse climates. To fully understand the paleoenvironmental significance of glendonites, a comprehensive examination of the modern ikaite setting is necessary. Temperature is the most important parameter that has been quantitatively constrained for the presence of ikaite. Low bottom-water temperature, while a required condition for formation of the mineral, is not adequate for its growth; other controls are necessary to explain the absence of ikaite in many cold environments. In this ...

An investigation of mineral dynamics in frozen seawater brines by direct measurement with synchrotron X‐ray powder diffraction

Abstract: Frozen seawater is a composite material with a sponge-like structure The framework of the structure is composed of pure ice, and within the pores exists a concentrated seawater brine When the temperature is reduced, the volume of this residual brine decreases, while its salinity increases As a result of the paired changes to temperature and salinity, the brine eventually becomes supersaturated with respect to a mineral, resulting in the precipitation of microscopic crystals throughout the ice structure Due to experimental constraints, the current understanding about the formation of these minerals relies on the analysis of the residual brine, rather than the mineral phase Here synchrotron X-ray powder diffraction was used to assess the dynamics that occur between ice, brine, and mineral phases within frozen seawater brines that were subjected to cooling and warming at subzero temperatures The method was able to detect crystalline phases of ice, mirabilite (Na2SO4·10H2O), and hydrohalite (NaCl·2H2O) Results illustrate a highly dynamic geochemical environment where ice-brine-mineral interactions tend toward an equilibrium crystallization process, which supports the process of seawater freezing that is described by the Gitterman Pathway and FREZCHEM model This study highlights the power of synchrotron techniques in observing the mineralogical dynamics of inaccessible environmental systems

Sediment inorganic carbon (PIC) deposits in seagrass meadows and adjacent sand-patches

Abstract: The database compiles published and unpublished data on carbonate (CaCO3) and/or particulate inorganic carbon (PIC) along with particulate organic carbon (POC) stocks if available, in sediments of seagrass meadows and adjacent un-vegetated patches. We considered the total pool of CaCO3 reported without distinguishing between the different biogenic carbonate mineral forms (calcite, Mg-calcite and aragonite). Fourqurean et al. (2012) provided data for 201 sites, and a literature search using both the Web of Knowledge (using the search terms “seagrass*” AND “inorganic carbon*” AND [“calcific* OR sediment* OR CaCO3 OR dissolut* OR diagenesis”]) and Google Scholar (using the search terms “seagrass carbonate”) yielded data for an additional 82 sites. The database was amended with unpublished values for 154 additional sites sampled by the authors. The database compiles data on sediment carbonate concentration for a total of 437 sites, of which 34 corresponded to sand patches adjacent to seagrass meadows. The final database comprises estimates for 403 seagrass vegetated sites, including 219 estimates for sediment surface samples (ca. 1-30 cm depth) and 184 estimates for sediment cores of variable length (149 cores < 100 cm-long, and 35 cores ≥ 100 cm-long). When only one of the variables, CaCO3 or PIC was reported, the other was estimated assuming that PIC is 12% of the total molar mass of the CaCO3. In most cases, particulate inorganic and organic carbon (PIC and POC) were reported as a percentage of dry weight (%DW), where PIC and POC, in mg cm-3, was calculated as the product of the fraction of sediment dry weight composed by PIC or POC and the dry bulk density (DBD) of a given sediment section (n = 340 sites). When DBD was not reported (n = 113 sites), we used the average DBD (1.03 g cm-3) reported by Fourqurean et al. (2012) for seagrass sediments in the calculations. Enquiries about the dabaset may be sent to Ines Mazarrasa .