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Oral Presentations of Section OS on Day 5 - Friday, August 07, 2015

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OS09 - Ocean Circulation and Climate Variability in the Eastern Indian Ocean
Friday, August 07, 2015 | 310 | 08:30-10:30
OS09-D5-AM1-310-001 (OS09-A013)
Diagnosis of the Mechanism of SST Seasonal Cycle South of Java
Weidong YU1#+, Yongliang DUAN2
1 Thailand-China Joint Laboratory for Climate and Marine Ecosystem, Thailand, 2 The First Institute of Oceanography, State Oceanic Administration, China
#Corresponding author: +Presenter

The variability of the sea surface temperature (SST) in the southeastern Indian Ocean plays a critical role in the Indonesian-Australian monsoon onset, the Indian Ocean Dipole and basin scale climate. However, the depression of seasonal SST in the Java Upwelling region is much smaller than that in the other eastern boundary upwelling regions. The mixed layer heat budget analysis based on high-resolution ocean data assimilation products and reanalysis data reveals that, during the coastal upwelling event (July-October), warm horizontal advection and the entrainment are out of phase. Furtherrmore, the negative feedback mechanism of SST–cloud–radiation plays a significant role in restricting the amplitude of seasonal SST variability. The surface heat flux, particularly the shortwave radiation helps SST.

OS09-D5-AM1-310-002 (OS09-A011)
Anomalies of Upwelling in the Eastern Indian Ocean: Possible Role of Secondary Circulation
Anastasia KUSWARDANI1#+, Tri Wahyu HADI2, Weidong YU3, Muhammad Arief RAHMAN4
1 Agency for Marine and Fisheries Research and Development, Indonesia, 2 Bandung Institute of Technology, Indonesia, 3 Thailand-China Joint Laboratory for Climate and Marine Ecosystem, Thailand, 4 Agency for Marine and Fisheries Research and Development/Institute For Marine Research And Observation, Indonesia
#Corresponding author: +Presenter

Eastern Indian Ocean in the south of Java Island is a large upwelling area, espcially during the east or southeast monsoon period of June through September. Observational data revealed that the upwelling off the southern coast of East Java is anomalously stronger compared to other areas accross the longitudes. We have calculated the magnitude of Ekman pumping over this area and the results show that the largest Ekman pumping with magnitude of 0.0265 N/m3 occurs in August off the southern coast of West Java. Moreover, the observed upwelling signal in this area and computed Ekman pumping show a positive correlation suggesting that the upwelling is predominantly induced by wind-driven transport. We have attempted to find plausible explanation for the upwelling anomalies off the southern coast of East Java by analyzing CTD data obtained during 22nd  September – 1st October 2013. In this paper, we discussed the effects of density gradients and stratification induced by mixing of water mass flux from the Indonesian Through Flow outlet of the Lombok strait. In addition, we also applied C-vector method to identify the possible role of frontal secondary circulation in enhancing upwelling in the studied area.

OS09-D5-AM1-310-003 (OS09-A012)
Analysis of Java Upwelling in the Indian Ocean Southwest of Java Based on the Stability of Water Mass
Agus SETIAWAN1#+, Gries Elvina NOOR2, Mukti TRENGGONO1, Mutiara Rachmat PUTRI2, Teguh AGUSTIADI1, Bayu PRIYONO1, Weidong YU3, Huiwu WANG4
1 Agency for Marine and Fisheries Research and Development, Ministry of Marine Affairs and Fisheries, Indonesia, 2 Institute Technology of Bandung, Indonesia, 3 Thailand-China Joint Laboratory for Climate and Marine Ecosystem, Thailand, 4 The First Institute of Oceanography, State Oceanic Administration, China
#Corresponding author: +Presenter

Identification of upwelling in the Indian Ocean southwest of Java was done based on the stability of water mass through the analysis of Brunt-Väisälä frequency (BVF). The BVF can be used to identify the stability of water mass that causes vertical movement. Data from Java Upwelling Variation Observations (JUVO) Project, research cooperation between Indonesia and China, were used in this study. These data consist of ocean current, conductivity, and temperature from subsurface mooring at 106.75° E – 8.5° S deployed from December 2008 to December 2013. The BVF profiles from 2008 to 2013 showed regular reduction that reached minimum or negative values during upwelling. During 2008 to 2010, the formation of upwelling in the Indian Ocean southwest of Java were started in June with BVF value of 1 x 10-4 s-1 and decreased to 6 x 10-5 s-1 in August or September (peak of upwelling). Upward vertical current with speed of 1.2 cm s-1 brings isotherm layer of 12° C and isohaline layer of 34.85 rise from a depth of 225 m to 190 m and 150 m, respectively. During the upwelling, mixed layer depth was depleted from 50 m to 30 m. IOD and ENSO phenomena also influence the formation time of upwelling in this area.

OS09-D5-AM1-310-004 (OS09-A010)
A Mid – Late Holocene Indian Winter Monsoon Variability Record from the Continental Shelf of Northeastern Sri Lanka
Kalpani RATNAYAKE1#+, Pradeep Nalaka RANASINGHE2,3, Liviu GIOSAN2, Stephan STEINKE4, Clive PONTON5, Mahyar MOHTADI6
1 University of Peradeniya, Sri Lanka, 2 Woods Hole Oceanographic Institution, United States, 3 University of Ruhuna, Sri Lanka, 4 1 MARUM - Center for Marine Environmental Sciences, University of Bremen, Germany, 5 University of Birmingham, United Kingdom, 6 University of Bremen, Germany
#Corresponding author: +Presenter

Northeastern continental shelf region of Sri Lanka is an important region to investigate Holocene Indian winter monsoon variability, because this region gets high terrigeneous input winter monsoon period while no such input is during the Indian summer monsoon. Although Sri Lanka is a sensitive region for climate changes, such studies to understand the mechanism of long term and short term climate variability are very scarce. We have carried out high-resolution marine proxy studies on a laminated marine sediment core from Pulmoddai (9o 03' 688", 81o03' 208" ,water depth 55 m) area situated in Northeastern continental shelf of Sri Lanka to reconstruct the winter monsoon-controlled precipitation, during the Holocene. Physical and chemical properties including chemical composition, color reflectance, magnetic susceptibility and d18O/16O and d 13C/12C ratios of Globigerinoids ruber foraminifera were measured to developed proxies. Radio carbon dates of micro scale mollusk shells were used to construct the age model. The data from direct proxies indicate the period from 5500-4000 cal yrs BP to present have generally increased terrestrial input and decreased salinity indicating increased monsoon activity despite of some short abrupt periods. The period between 4000-1500 have a decreased terrestrial indicating decreased monsoon activity. This results indicate that winter monsoon variability is in phase with summer monsoon variability of the region.

OS09-D5-AM1-310-005 (OS09-A008)
Deep Meridional Overturning Circulation in the Indian Ocean and its Relation to Indian Ocean Dipole
Weiqiang WANG1#+, Xiuhua ZHU2, Chunzai WANG3, Armin KOEHL2
1 South China Sea Institute of Oceanology, China, 2 Center fur Erdsystemforschung und Nachhaltigkeit, KlimaCampus, University of Hamburg, Germany, 3 NOAA Atlantic Oceanographic and Meteorological Laboratory, United States
#Corresponding author: +Presenter

The Indian Ocean deep meridional overturning circulation (DMOC) and its relation to the Indian Ocean dipole mode (IOD) are examined. Contributions of various dynamical processes are assessed by decomposing the DMOC into the Ekman and geostrophic transport, the external mode, and a residual term. The first three terms successfully describe the DMOC with a marginal residual term. The following conclusions are obtained. First, the seasonal cycle of the DMOC is mainly determined by the Ekman component. The exception is during the transitional seasons (March–April and September–October) in the northern Indian Ocean Basin, where the geostrophic component dominates. Second, at the beginning phase of the IOD (May–June), the Ekman component dominates the DMOC structure; at and after the peak phase of the IOD (September–December), the DMOC structure is primarily determined by the geostrophic component in correspondence with the well-developed sea surface temperature anomalies, while the wind (and thus the Ekman component) plays a secondary role south of 10S and contributes negatively within the zonal band of 10S on both sides of the equator. Therefore, there exists a surface to deep-ocean connection through which IOD-related surface wind and ocean temperature anomalies are transferred down to the deep ocean. Westward-propagating signals are observed even in the deep ocean, suggesting possible roles of Rossby waves in transferring the surface signal to the deep ocean.

OS09-D5-AM1-310-006 (OS09-A016)
Ventilation Processes of the Tropical Eastern Indian Ocean Based on CFC-11 and CFC-12 Measurements
Minggang CAI#, Hengxiang DENG+, Hongwei KE, Peng HUANG
Xiamen University, China
#Corresponding author: +Presenter

Transient tracers are the compounds that have a time-dependent concentration and can be explored to study on circulation and ventilation time-scales. Our working group is mainly working with the chlorofluorocarbon (i.e., CFCs), and the sulfur hexafluoride (i.e., SF6). These compounds are released to the atmosphere and enter the ocean through air-sea exchange. Measurements of these compounds in the ocean is the focus of our practical job, and then this information can be used to calculate properties like the mean age of a water mass, or the concentration of anthropogenic CO2 (Cant).In this study, based on the measurements of the transient tracers CFC-11 and CFC-12 made in the tropical eastern Indian Ocean, the transit time distribution (TTD) concept was used to calculate ventilation time-scales and the concentration of anthropogenic CO2 (Cant). The CFC-11 and CFC-12 concentrations decrease monotonously with the depth and the deep water has CFC-11 and CFC-12 values close to the detection limit. The ventilation time (mean ages) for the deep water column are calculated, while the total Cant inventory (referenced to year 2012) was also estimated.

OS09-D5-AM1-310-007 (OS09-A009)
The Effects of Wind Forcing on Surface Currents on the Rottnest Continental Shelf, Western Australia
Jennifer PENTON#+
The University of Western Australia, Australia
#Corresponding author: +Presenter

Surface currents play a major role in the distribution of contaminants, the connectivity of marine populations, the planning of navigational routes, and can influence the vertical and horizontal distribution of nutrients within the water column. Whilst general current patterns have been well researched and documented, surface currents, commonly forming eddies and opposing flow direction, have not. With the increase of FLNG plants, the importance of profound knowledge and accuracy on the surface currents is also increasing. This paper aims to determine the effects of sea breeze-wind patterns, as well as seasonal storm events, on the climatology of the surface currents on the continental shelf surrounding Rottnest Island, Western Australia. The alternating wind patterns allow for full cyclic rotations of wind direction at near storm-strength forces, permitting the interpretation of the effect of the wind on the surface currents, whilst the bathymetrical patterns allow for recurring surface current patterns to be implicated onto other regions of interest.

Using HF radar data, it was found that the surface currents only clearly follow the northbound Capes Current in times when the southerly winds of the daily sea breeze sets in. During periods of full cyclic directional rotations of strong wind, surface currents react within an hour to a change of direction of the wind, often followed by mixed currents as the wind dies down. During storm events the surface currents follow suit of the wind, after which the currents maintain the same direction longer than the wind persists. Complex correlations suggest that a longer wind duration in a consistent direction will have a stronger impact on the surface currents, forcing them to a deeper potential. Summer and winter storm events have been shown to have opposing effects on local eddies, the winter storms leading to their decimation, summer storms encouraging their spin up.

OS09-D5-AM1-310-008 (OS09-A014)
Spatial Variation of Sea Level Anomalies in the Eastern Indian Ocean and Southern South China Sea
Soumya MOHAN1+, Vethamony P1#, Pavel TKALICH2
1 National Institute of Oceanography, India, 2 National University of Singapore, Singapore
#Corresponding author: +Presenter

Sea level anomalies (SLAs) derived from satellite observations (over a period of 20 years) and tide gauge data compiled from 22 stations from the eastern Indian Ocean (EIO) and southern South China Sea (SSCS) have been analysed to study the spatial variation of SLAs in the EIO and SSCS. SLAs were further decomposed into linear trend, mean seasonal cycle and non-seasonal components. Spatial pattern, representing the contribution of each component, shows that linear trend variations could explain ~10% of variance in EIO and SSCS; non-seasonal sea level variability accounts for ~70% variability off Sumatra and ~50% in the Andaman Sea and Malacca Strait, whereas, seasonal variability of SLA is higher in the SSCS and Gulf of Thailand. Spatial patterns of sea level variability on the eastern boundary of the Indian Ocean exhibit non-coherent variability with SSCS, but show coherent variability with western Pacific. Empirical orthogonal function (EOF) analysis of non-seasonal SLAs in the EIO and SSCS shows that the first mode is related to interannual variations, and strongly correlated to Dipole mode index (DMI). Indian Ocean Dipole (IOD) spatial signature is observed in the EIO, Malacca Strait and Singapore Strait, and it gradually weakens in the SSCS. The seasonal sea level cycle is found to be very different in the Andaman Sea and SSCS. The non-seasonal SLAs in the Malacca Strait and SSCS are least correlated. We find coherent variability in interannual SLAs in the Bay of Bengal, Andaman Sea and Malacca Strait.

OS09-D5-AM1-310-009 (OS09-A003)
Freshening of the Indonesian Throughflow and the Leeuwin Current During the 2010-11 La Niña/Ningaloo Niño
Ming FENG#+
CSIRO Oceans and Atmosphere Flagship, Australia
#Corresponding author: +Presenter

During the 2010-11 La Niña/Ningaloo Niño, excessive precipitations in the Maritime continent and Indonesian-Australia Basin have caused a 0.3 psu freshening of the surface waters in the southeast Indian Ocean. The freshening anomalies are carried westward by the Indonesian Throughflow and the South Equatorial Current, and carried southward along the Western Australia coast by the poleward flowing eastern boundary current, the Leeuwin Current. Salinity anomalies contribute to more than 20% of the anomalous increase of the southward Leeuwin Current transport at the peak of the 2010-11 Ningaloo Niño, resulting unprecedented warming of the coast of Western Australia. Episodically freshening of the Leeuwin Current has been observed at a coastal reference station off Western Australia during extended La Nina conditions over the past several decades.

OS12 - General Oceanography
Friday, August 07, 2015 | 310 | 11:00-12:30
OS12-D5-AM2-310-001 (OS12-A003)
The Early Winter Sea Ice Variability Under the Recent Arctic Climate Shift
Xiao-Yi YANG#+
Xiamen University, China
#Corresponding author: +Presenter

This study reveals that sea ice in the Barents and Kara Seas plays a crucial role in establishing a new Arctic coupled climate system. The early winter sea ice before 1998 shows double dipole patterns over the Arctic peripheral seas. This pattern, referred as the early winter quadrupole pattern, exhibits the anti-clockwise sequential sea ice anomalies propagation from the Greenland Sea, the Barents-Kara Seas, to the Bering Sea from October to December. This early winter in-phase ice variability contrasts to the out-of-phase relationship in the late winter. The mean temperature advection and stationary wave heat flux divergence associated with the atmospheric zonal wave-2 pattern are responsible for the early winter in-phase pattern.

Since the end of last century, the early winter quadrupole pattern has broken down due to the rapid decline of sea ice extent in the Barents-Kara Seas. This remarkable ice retreat modifies the local ocean-atmosphere heat exchange, forcing an anomalous low air pressure over the Barents-Kara Seas. The subsequent collapse of the atmospheric zonal wave-2 pattern is likely responsible for the breakdown of the early winter sea ice quadrupole pattern after 1998. Therefore, the sea ice anomalies in the Barents-Kara Seas play a key role in establishing new atmosphere-sea ice coupled relationships in the warming Arctic.

OS12-D5-AM2-310-002 (OS12-A021)
Geostrophic Variation of Circum-Antarctica Sea Level Observed by GRACE in Relation to the Antarctica Oscillation
Benjamin Fong CHAO#+, J. R. LIAU
Academia Sinica, Taiwan
#Corresponding author: +Presenter

The Antarctic Oscillation (AAO) in the atmosphere and the Antarctic Circumpolar Current (ACC) in the oceans dominate the meteorological system of the mid-to-high latitude Southern Hemisphere. They are linked via the cause-and-effect scenario from westerly wind field on to the zonal geostrophic ocean currents. Here we establish unequivocally the link between the space-time behavior of AAO and ACC in their entirety, using the time-variable gravity data from the twin-satellite mission Gravity Recovery and Climate Experiment (GRACE) during 2003-2014. We find the non-seasonal dynamic height of the circum-Antarctica seas, in the leading mode of the empirical orthogonal function (EOF) solution, varies in close pace with the AAO Index with a correlation as high as 0.80. This variation gives rise to variation in the surface geostrophic current with spatial pattern matching that of ACC itself, and oscillating according to AAO in such a manner that the east-component of ACC strengthens when the AAO Index increases positively. It is further verified that as the AAO Index grows more positive (with stronger westerlies) over the years, the resultant strengthening of ACC shifts poleward decisively, contracting its circum-Antarctica ring pattern. This study represents a first utility of the GRACE observations in revealing on the geostrophic dynamics of the oceans.

OS12-D5-AM2-310-003 (OS12-A022)
Humpback Whale Distribution Relative to Environmental Conditions
Griffith University, Australia
#Corresponding author: +Presenter

Humpback whales, Megaptera novaeangliae, take part in the largest annual migration of any mammal, from polar feeding grounds in summer to tropical breeding grounds in winter. A large part of this migration takes place near the coast in waters heavily influenced by human activity. This results in exposure to a number of threats including stranding, entanglement, pollution and interactions with boats. Protection from these threats, as well as understanding how climate change is likely to affect humpback whales, will require detailed knowledge of preferred habitat and the reasons behind the preferences.

The large scale migration patterns of humpback whales are fairly well known; however, small scale distribution patterns and relationships with environmental conditions have received less attention. Studies on feeding grounds have found preferences for areas with upwelling and strong gradients of temperature, depth and currents, while preferred conditions on breeding grounds are shallow, warm areas with slow water movement. Preferences for resting areas and migration routes are unknown.

The east Australian coastal environment is dominated by the East Australian Current, the western boundary current of the South Pacific Ocean, carrying warm water poleward from the tropics. This current, as well as strong northerly winds, generates upwelling on the coast and provides nutrients for primary production. This study investigates relationships between humpback whale distribution and environmental conditions while migrating and resting on the Gold Coast, Australia. Whale distribution was surveyed from land and boats and will be compared with a range of environmental parameters measured in situ, remotely sensed and modelled.

Analysis is in progress, early results suggest a preference for cooler waters and in areas with a strong temperature gradient. The higher productivity in cooler upwelled waters and frontal zones may provide the migrating whales with a chance of opportunistic feeding, a rare occurrence on their massive journey.

OS12-D5-AM2-310-004 (OS12-A023)
Physical Drivers Affecting the Catchability of Spanner Crabs (Ranina Ranina) in Eastern Australian Waters
David SPENCER1#+, Charles LEMCKERT1, Ian BROWN2, Shing Yip LEE1
1 Griffith University, Australia, 2 Fisheries Queensland, Australia
#Corresponding author: +Presenter

Fisheries are highly valuable resources worldwide, continually growing to meet increasing demand. As these industries expand, they need to be closely monitored before their harvests exceed sustainable levels. Few studies focus on the ideal physical conditions in which the fishery species thrives. My research aims to quantify the relationship between physical oceanographic variables and the catchability of an important commercial fisheries resource: the Australian spanner crab (Ranina ranina)

Preliminary studies provide good insight that both large scale processes and small scale processes may be affecting spanner crab catchability. How large scale processes have affected spanner crab catch rates will be analysed using historical CPUE, and satellite wind, SST, and altimetry data. Analysing the wind and oceanographic data will help determine whether processes such as upwelling, downwelling, and mesoscale eddy formation are responsible for some of these catch variations.

In situ observations made using an ADV, ADCP, CTD, and small temperature sensors will also be used to help explain changes in spanner crab catch. This method provides a much more accurate assessment of any relationships between CPUE and oceanographic processes, as oceanographic instruments have the advantage of providing “true field data” and the accuracy of total spanner crab catch will be improved whilst counts are made on board a commercial spanner crab fishing vessel. Bottom ambient temperature and current data will be used in a liner mixed-effect model, investigating the combined effects these data have on spanner crab catch rates. Periods of particular interest include instances with significant temperature and current velocity variations, enabling analysis on the obvious changes in the physical state of the bottom boundary layer. On completion of the project, a much greater insight into the effects of physical drivers on past and current spanner crab catchability will have been achieved.

OS12-D5-AM2-310-005 (OS12-A015)
The Florida Current in Stream Coordinates: On the Effects of Meandering at 25°N to 26°N
Matthew R. ARCHER#+, Lynn K. SHAY
Rosenstiel School of Marine and Atmospheric Science, University of Miami, United States
#Corresponding author: +Presenter

While the mean horizontal structure of the Florida Current has been well documented, its variability in time is still not fully understood. How does the horizontal structure of the Current vary on a time scale of hours to days? What is the horizontal pattern of kinetic energy exchange across the Current, and how does lateral meandering influence this? We address these questions using surface current velocity measurements from high frequency (HF) radar, and an in situ velocity profile timeseries from Nortek’s 600 KHz acoustic wave and current (AWAC) profiler.

The HF radar is a phased-array WERA system, operating at 16.045 MHz along the Southeast Florida coastline, with a resolution of 20-min and 1.2-km in time and space, and a range of 80-km. Since the Florida Current flows northward through the center of the HF radar footprint, we can accurately determine its mean horizontal structure and hourly variability in offshore position (meandering), core intensity, width, and lateral shear.

We convert the data from a longitude/latitude grid to stream coordinates, in which the origin is fixed to the core of the jet rather than a geographical location. In stream coordinates we calculate a more realistic time average, which is unaffected by the lateral meandering of the jet. By removing meandering, we can investigate if there are any systematic changes in the horizontal velocity structure during the meander crest/trough, and during times with no meander. We quantify the contribution of meandering to surface eddy kinetic energy and momentum flux, and discuss the variability and associated errors of these terms.

OS12-D5-AM2-310-006 (OS12-A025)
Evolution of Distribution of Methane Hydrates in the Northern South China Sea Since the Last Glacial Maximum
Lihua LIU1#+, Nengyou WU2, Haibing SHAO3, Shaoying FU4
1 Chinese Academy of Sciences, China, 2 Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, China, 3 Helmholtz Centre for Environmental Research GmbH - UFZ, Germany, 4 Guangzhou Marine Geology Survey, China
#Corresponding author: +Presenter

The distribution and inventory of gas hydrates in a region is determined by the sediment characteristics, methane supply and evolution of the reservoir. In recent decades, the geo-environmental constraints and sources of methane have been intensively investigated. However, information regarding the evolution of hydrate reservoirs remains limited. This study developed a simulator to model the evolution of specific reservoirs that were deposited in the Northern South China Sea (NSCS) since the Last Glacial Maximum (LGM). The LGM was a recent cold epoch that occurred approximately 18,000 years ago. Since the LGM, the earth’s climate system has experienced a continuous increase of surface temperature and rising sea level. Given a sufficient supply of methane and a transport system, hydrates may form in marine sediments if sea level rises or melt if the temperature increases. A one-dimensional simulator that represents the sediment was developed and uses the current hydrate profiles as the initial conditions and reliable paleoenvironmental data as boundary conditions. Two types of hydrate profiles were reversely simulated till the LGM: (i) a Gaussian profile, which was observed in the Shenhu area, and (ii) a trapezoidal profile, which was observed in the Dongsha area. The evolution and past quantities of local hydrate reservoirs were estimated. The model results demonstrated that shallow (500-700 meters below the seafloor, or mbsf) moderate-saturation (50% pore volume, or v:v) hydrate deposits will form if they are subjected to recent climate changes. The inventory of hydrates in the NSCS increased by only 0 to 7 % over the past 18,000 years under different scenarios.