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2019-20 Honours project - Characterising the variability of the Indonesian Throughflow in ocean models
The Indonesian Throughflow (ITF) is connects the Pacific Ocean and the Indian Ocean in the tropics. The ITF plays an essential role in ocean circulation and regional climate: it hosts strong mixing that can change water-mass properties, influences the sea surface temperature in both oceans and affects the global ocean volume and heat transports. The ITF transports water properties across Indonesian Seas characterized by complex topography with most of the water entering through two main inflow straits, Makassar and Lifamatola straits, and exiting into the Indian Ocean through three main outflow straits, Ombai, Lombok and Timor straits. The ITF shows variabilities on different time scales, including decadal, interannual, seasonal and intra-seasonal. The ITF variability on intra-seasonal time scales is driven by remotely generated Kelvin and Rossby waves that propagate into the Indonesian Seas from the Indian Ocean and Pacific Ocean. This project focuses on the variability driven by Kelvin waves that propagate into Indonesian seas through three main outflow straits (Ombai, Lombok and Timor). We use a global ocean model and a high-resolution regional ITF model to characterize these variabilities at different depths and in different straits. We also use the mooring observations from the INSTANT program to validate the ocean models.
Phytoplankton productivity in the polar Southern Ocean (SO) plays an important role in the transfer of carbon from the atmosphere to the ocean’s interior, a process called the biological carbon pump, which helps regulate global climate. SO productivity in turn is limited by low iron, light, and temperature, which restrict the ef- ficiency of the carbon pump. Iron and light can colimit productivity due to the high iron content of the photosynthetic photosystems and the need for increased photosystems for low-light acclimation in many phytoplankton. Here we show that SO phytoplankton have evolved critical adaptations to enhance photosynthetic rates under the joint constraints of low iron, light, and temperature. Under growth-limiting iron and light levels, three SO species had up to sixfold higher photosynthetic rates per photosystem II and similar or higher rates per mol of photosynthetic iron than tem- perate species, despite their lower growth temperature (3 vs. 18 °C) and light intensity (30 vs. 40 μmol quanta·m2·s−1), which should have decreased photosynthetic rates. These unexpectedly high rates in the SO species are partly explained by their unusually large photosynthetic antennae, which are among the largest ever recorded in marine phytoplankton. Large antennae are disadvan- tageous at low light intensities because they increase excitation energy loss as heat, but this loss may be mitigated by the low SO temperatures. Such adaptations point to higher SO production rates than environmental conditions should otherwise permit, with implications for regional ecology and biogeochemistry.
This record provides an overview of the NESP Marine and Coastal Hub bridging study - "Future-proofing restoration & thermal physiology of kelp". For specific data outputs from this project, please see child records associated with this metadata. -------------------- For restoration to be effective, the cause of habitat decline must be understood and overcome. But this is problematic when climate change is driving habitat loss since it cannot be reversed or ameliorated prior to restoration. A previous NESP project led by this team (Project E7, Marine Biodiversity Hub) identified warmwater-tolerant strains of giant kelp from remnant patches in eastern Tasmania, where the species has experienced precipitous declines due to ocean-warming. These strains have high potential to assist with ‘future-proofing’ kelp forest restoration, however it is still unclear what the physiological mechanisms are that provide their improved thermal tolerance. This project is designed to better understand these physiological mechanisms to advance kelp restoration efforts in Australia and globally, and progress toward the identification of populations of Australian kelp that may be resilient to (or especially threatened by) ocean warming and climate change. Planned Outputs • Ecophysiological measurements from laboratory experiments of warm-tolerant vs average giant kelp genotypes [dataset] • Final technical report with analysed data, including a short summary of recommendations for policy makers of key findings [written]
Intraspecific variation in the thermal tolerance of microscopic giant kelp (Macrocystis pyrifera) sporophytes was tested using a common garden experiment, where 49 unique family-lines were raised under four different water temperatures (12, 16, 20, and 24°C). The unique family-lines were taken from ongoing giant kelp gametophyte cultures held at IMAS, and represented F1 offspring from seven 'selfed' individuals collected from 6 sites across ~250km in Tasmania, Australia, in addition to a site-level cross from each of the sites, and a panmictic cross using the 42 pure family lines. Survivorship of the selected warm-adapted family-lines after outplanting trials at restoration sites can be found here with the associated dataset "NESP Marine Hub Project E7 outplanted kelp survivorship". https://metadata.imas.utas.edu.au/geonetwork/srv/eng/catalog.search#/metadata/908afd8c-cc7a-4ea3-a87e-4497ae8da87a