Impact of the barotropic tides on the seasonal Indonesian Throughflow

The Indonesian seas play a fundamental role in the coupled climate system, featuring the only tropical exchange between ocean basins in the global thermohaline circulation. The Indonesian Throughflow (ITF) carries Pacific Ocean warm pool waters through the Indonesian Seas, where they are cooled and freshened. The incoming Pacific waters are strongly modified via vertical mixing driven by numerous ocean processes and ocean-atmosphere fluxes. The result is a unique water mass that can be tracked across the Indian Ocean basin and beyond. With our high-resolution regional model of the Indonesian Seas, designed with the MITgcm, we focus our study on the impact of the barotropic tides on the ITF. In fact, the strong tides coming from the Pacific and Indian Oceans enter in the Indonesian Seas through narrow straits and interact with the complex topography of the region (sills, islands, deep seas). This interaction between the tides and the topography impacts directly the ITF by modifying the transport toward the Indian Ocean.

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Impact of Indo-Pacific Feedback Interactions on ENSO Dynamics Diagnosed Using Ensemble Climate Simulations

Journal of Climate ◽

10.1175/jcli-d-11-00287.1 ◽

2012 ◽

Vol 25 (21) ◽

pp. 7743-7763 ◽

Cited By ~ 49

Author(s):

A. Santoso ◽

M. H. England ◽

W. Cai

Keyword(s):

Indian Ocean ◽

Climate Model ◽

Southern Oscillation ◽

Ocean Basin ◽

Climate Feedback ◽

Enso Events ◽

Thermocline Feedback ◽

Enso Dynamics ◽

The Indian Ocean ◽

The Impact

The impact of Indo-Pacific climate feedback on the dynamics of El Niño–Southern Oscillation (ENSO) is investigated using an ensemble set of Indian Ocean decoupling experiments (DCPL), utilizing a millennial integration of a coupled climate model. It is found that eliminating air–sea interactions over the Indian Ocean results in various degrees of ENSO amplification across DCPL simulations, with a shift in the underlying dynamics toward a more prominent thermocline mode. The DCPL experiments reveal that the net effect of the Indian Ocean in the control runs (CTRL) is a damping of ENSO. The extent of this damping appears to be negatively correlated to the coherence between ENSO and the Indian Ocean dipole (IOD). This type of relationship can arise from the long-lasting ENSO events that the model simulates, such that developing ENSO often coincides with Indian Ocean basin-wide mode (IOBM) anomalies during non-IOD years. As demonstrated via AGCM experiments, the IOBM enhances western Pacific wind anomalies that counteract the ENSO-enhancing winds farther east. In the recharge oscillator framework, this weakens the equatorial Pacific air–sea coupling that governs the ENSO thermocline feedback. Relative to the IOBM, the IOD is more conducive for ENSO growth. The net damping by the Indian Ocean in CTRL is thus dominated by the IOBM effect which is weaker with stronger ENSO–IOD coherence. The stronger ENSO thermocline mode in DCPL is consistent with the absence of any IOBM anomalies. This study supports the notion that the Indian Ocean should be viewed as an integral part of ENSO dynamics.

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Pathways and Effects of the Indonesian Throughflow Water in the Indian Ocean Using Particle Trajectory and Tracers in an OGCM

Journal of Climate ◽

10.1175/jcli4167.1 ◽

2007 ◽

Vol 20 (13) ◽

pp. 2994-3017 ◽

Cited By ~ 31

Author(s):

Vinu K. Valsala ◽

Motoyoshi Ikeda

Keyword(s):

Indian Ocean ◽

Vertical Mixing ◽

Surface Current ◽

Western Boundary ◽

Indonesian Throughflow ◽

Somali Region ◽

High Salinity Water ◽

The North ◽

The Indian Ocean ◽

Passive Tracers

Abstract The 3D pathways of the Indonesian Throughflow (ITF) in the Indian Ocean are identified using an OGCM, with a combined set of tools: 1) Lagrangian particle trajectories, 2) passive tracers, and 3) active tracers (temperature and salinity). Each of these tools has its own advantages and limitations to represent the watermass pathways. The Lagrangian particles, without horizontal and vertical mixing, suggest that at the entrance region the surface ITF subducts along the northwestern coast of Australia and then travels across the Indian Ocean along the thermocline depths. The subsurface ITF more directly departs westward and crosses the Indian Ocean. Using the passive tracers, which are mixed vertically under convection as well as horizontally due to diffusion, the ITF is shown to undergo vigorous mixing as soon as it enters the Indian Ocean and modifies its upper temperature–salinity (T–S) characteristics. Thus, the surface and subsurface ITF watermasses lose their identities. Upon reaching the western boundary, the ITF reroutes into three distinct depth ranges, owing to the seasonal reversal of the Somali region: route 1—across the Indian Ocean just to the south of the equator (200–300 m); route 2—across the Indian Ocean to the north of the equator (100–200 m); and route 3—upwells in the Somali region and spreads all over the surface of the northern Indian Ocean. The seasonality of the Somali Current is crucial to spread the ITF along route 3 during the summer monsoon (April–October) and route 2 during the winter monsoon (November–March). The basinwide spreading is responsible for a long residence time of the ITF in the Indian Ocean to be at least 20 yr. The effects of the ITF on the temperature and salinity are mainly accompanied with the major pathways. However, indirect effects are visible in a few spots; that is, the warm and saline feature is produced in the subsurface off the southwestern coast of Australia around 30°S caused by the eastward surface current, which is under the thermal wind relationship owing to the warm and fresh ITF component. This component also enhances vertical convection and warms the surface around 40°S. The Arabian Sea high salinity water is produced extensively with the effects of the Somali upwelling, which is originally strengthened by the fresh and warm ITF.

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Anthropogenic iron deposition alters the ecosystem and carbon balance of the Indian Ocean over a centennial timescale

10.5194/egusphere-egu2020-21916 ◽

2020 ◽

Author(s):

Anh Pham ◽

Takamitsu Ito

Keyword(s):

Indian Ocean ◽

Arabian Sea ◽

Ocean Basin ◽

Ecosystem Dynamics ◽

Carbon Uptake ◽

The South ◽

Nutrient Deposition ◽

The North ◽

The Indian Ocean ◽

The Impact

Phytoplankton growth in the Indian Ocean is generally limited by macronutrients (nitrogen: N and phosphorus: P) in the north and by micronutrient (iron: Fe) in the south. Increasing anthropogenic atmospheric deposition of N and dissolved Fe (dFe) into the ocean can thus lead to significant responses from marine ecosystems in this ocean basin. Previous modeling studies investigated the impacts of anthropogenic nutrient deposition on the ocean, but their results are uncertain due to incomplete representations of Fe cycling. We use a state-of-the-art ocean ecosystem and Fe cycling model to evaluate the transient responses of ocean productivity and carbon uptake in the Indian Ocean, focusing on the centennial time scale. The model incorporates all major external sources and represents a complicated internal cycling process of Fe, thus showing significant improvements in reproducing observations. Sensitivity simulations show that after a century of anthropogenic deposition, increased dFe stimulates diatoms productivity in the southern Indian Ocean poleward of 50&#8304;S and the southeastern tropics. Diatoms production weakens in the south of the Arabian Sea due to the P limitation, and diatoms are outcompeted there by coccolithophores and picoplankton, which have a lower P demand. These changes in diatoms and coccolithophores productions alter the balance between the organic and carbonate pumps in the Indian Ocean, increasing the carbon uptake in the south of 50&#8304;S and the southeastern tropics while decreasing it in the Arabian Sea. Our results reveal the important role of ecosystem dynamics in controlling the sensitivity of carbon fluxes in the Indian Ocean under the impact of anthropogenic nutrient deposition over a centennial timescale.

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Indo-Pacific Climate Interactions in the Absence of an Indonesian Throughflow

Journal of Climate ◽

10.1175/jcli-d-14-00114.1 ◽

2015 ◽

Vol 28 (13) ◽

pp. 5017-5029 ◽

Cited By ~ 12

Author(s):

Jules B. Kajtar ◽

Agus Santoso ◽

Matthew H. England ◽

Wenju Cai

Keyword(s):

Indian Ocean ◽

Climate Model ◽

Southern Oscillation ◽

Ocean Basin ◽

Climate System ◽

Indonesian Throughflow ◽

Enso Events ◽

The Pacific ◽

The Indian Ocean ◽

Mean Climate

Abstract The Pacific and Indian Oceans are connected by an oceanic passage called the Indonesian Throughflow (ITF). In this setting, modes of climate variability over the two oceanic basins interact. El Niño–Southern Oscillation (ENSO) events generate sea surface temperature anomalies (SSTAs) over the Indian Ocean that, in turn, influence ENSO evolution. This raises the question as to whether Indo-Pacific feedback interactions would still occur in a climate system without an Indonesian Throughflow. This issue is investigated here for the first time using a coupled climate model with a blocked Indonesian gateway and a series of partially decoupled experiments in which air–sea interactions over each ocean basin are in turn suppressed. Closing the Indonesian Throughflow significantly alters the mean climate state over the Pacific and Indian Oceans. The Pacific Ocean retains an ENSO-like variability, but it is shifted eastward. In contrast, the Indian Ocean dipole and the Indian Ocean basinwide mode both collapse into a single dominant and drastically transformed mode. While the relationship between ENSO and the altered Indian Ocean mode is weaker than that when the ITF is open, the decoupled experiments reveal a damping effect exerted between the two modes. Despite the weaker Indian Ocean SSTAs and the increased distance between these and the core of ENSO SSTAs, the interbasin interactions remain. This suggests that the atmospheric bridge is a robust element of the Indo-Pacific climate system, linking the Indian and Pacific Oceans even in the absence of an Indonesian Throughflow.

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Indo-Pacific warm pool expansion modulates MJO lifecycle

10.5194/egusphere-egu2020-1039 ◽

2020 ◽

Author(s):

Panini Dasgupta ◽

Roxy Mathew Koll ◽

Michael J. McPhaden ◽

Tamaki Suematsu ◽

Chidong Zhang ◽

...

Keyword(s):

Life Cycle ◽

Indian Ocean ◽

Southern Oscillation ◽

Average Rate ◽

Warm Pool ◽

Dominant Mode ◽

Maritime Continent ◽

Pacific Warm Pool ◽

The Indian Ocean ◽

The Impact

The Madden&#8211;Julian Oscillation (MJO) is the most dominant mode of intraseasonal variability in the tropics, characterized by an eastward propagating zonal circulation pattern and rain bands. MJO is very crucial phenomenon due to its interactions with other timescales of ocean-atmosphere like El Ni&#241;o Southern Oscillation, tropical cyclones, monsoons, and the extreme rainfall events all across the globe. MJO events travel almost half of the globe along the tropical oceans, majorly over the Indo-Pacific Warm Pool (IPWP) region. This IPWP region has been warming during the twentieth and early twenty- first centuries in response to increased anthropogenic emissions of greenhouse gases and is projected to warm further. However, the impact of the warming of the IPWP region on the MJO life cycle is largely unknown. Here we show that rapid warming over the IPWP region during 1981&#8211;2018 has significantly changed the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3&#8211;4 days, and increasing over the Indo-Pacific Maritime Continent by 5&#8211;6 days. We find that these changes in the MJO life cycle are associated with a twofold expansion of the Indo-Pacific warm pool. The warm pool has been expanding on average by 2.3 &#215; 105 km2 per year during 1900&#8211;2018 and at an accelerated average rate of 4 &#215; 105 km2 per year during 1981&#8211;2018. The accelerated warm pool expansion has increased moisture in the lower and middle troposphere over IPWP and thereby increased the gradient of lower-middle tropospheric moisture between the Indian Ocean and western Pacific. This zonal gradient of moisture between the Indian Ocean and west Pacific and the increased subsidence over the Indian ocean due to increased convective duration of MJO over maritime continent are likely the reasons behind the changing lifecycle of MJO.

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Seasonal and Interannual Variability of the Indo-Pacific Warm Pool and its Associated Climate Factors Based on Remote Sensing

Remote Sensing ◽

10.3390/rs12071062 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1062 ◽

Cited By ~ 2

Author(s):

Zi Yin ◽

Qing Dong ◽

Fanping Kong ◽

Dan Cao ◽

Shuang Long

Keyword(s):

Pacific Ocean ◽

Indian Ocean ◽

Time Scale ◽

Warm Pool ◽

Ocean Basin ◽

The Pacific ◽

Pacific Warm Pool ◽

The Indian Ocean ◽

The Pacific Ocean ◽

Ocean Sector

With satellite observed Sea Surface Temperature (SST) accumulated for multiple decades, multi-time scale variabilities of the Indo-Pacific Warm Pool are examined and contrasted in this study by separating it into the Indian Ocean sector and the Pacific Ocean sector. Surface size, zonal center, meridional center, maximum SST and mean SST as the practical warm pool properties are chosen to investigate the warm pool variations for the period 1982–2018. On the seasonal time scale, the oscillation of the Indian Warm Pool is found much more vigorous than the Pacific Warm Pool on size and intensity, yet the interannual variabilities of the Indian Warm Pool and the Pacific Warm Pool are comparable. The Indian Warm Pool has weak interannual variations (3–5 years) and the Pacific Warm Pool has mighty interdecadal variations. The size, zonal movement and mean SST of the Indian Ocean Warm Pool (IW) are more accurate to depict the seasonal variability, and for the Pacific Ocean Warm Pool (PW), the size, zonal and meridional movements and maximum SST are more suitable. On the interannual scale, except for the meridional movements, all the other properties of the same basin have similar interannual variation signals. Following the correlation analysis, it turns out that the Indian Ocean basin-wide index (IOBW) is the most important contributor to the variabilities of both sectors. Lead-lag correlation results show that variation of the Pacific Ocean Warm Pool leads the IOBW and variation of the Indian Ocean Warm Pool is synchronous with the IOBW. This indicates that both sectors of the Indo-Pacific Warm Pool are significantly correlated with basin-wide warming or cooling.

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Were springline carbonates in the Kurkur-Dungul area (Southern Egypt) deposited during glacial periods?

Journal of the Geological Society ◽

10.1144/jgs2020-147 ◽

2020 ◽

pp. jgs2020-147

Author(s):

Sándor Kele ◽

Emad S. Sallam ◽

Enrico Capezzuoli ◽

Mike Rogerson ◽

Hamdalla Wanas ◽

...

Keyword(s):

Indian Ocean ◽

Sea Level ◽

Warm Pool ◽

Source Water ◽

Indonesian Throughflow ◽

Orbital Forcing ◽

Western Margin ◽

The Indian Ocean ◽

Glacial Periods ◽

Aquifer Flow

The tufa deposits in the Kurkur–Dungul area, southern Egypt, date from marine isotope stage (MIS) 11 to MIS 1. Springs across the region were active during glacial periods (with sea level below –50 m), reflecting changed atmospheric circulation over the Indian Ocean, as well as peak interglacial periods. During times of low sea level, reduced Indonesian throughflow promoted formation of an Indian Ocean Warm Pool, and anomalous rainfall on its western margin. We suggest Egypt lies at the intersection of westerly (“maghrebian”) and easterly (“mashriqian”) rainfall provinces, which show different timing with relation to orbital forcing and different source water regions. Tufa-growth periods are therefore not mechanistically linked to “humid periods” or “sapropel events” identified elsewhere. Stable isotope and TΔ47 data are also inconsistent with these spring systems being part of a larger system spanning northern Africa, and lack a clear interaction between northern hemisphere heating and mid-latitude rainfall. We also follow previous authors in concluding that formation of springline deposit formation was likely delayed compared to rainfall, due to aquifer flow distances. This delay is unlikely sufficient to explain why rainfall is out of phase movements of the monsoon belts, but may complicate interpretation of these records.

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Spatiotemporal Evolution and Determinant Factors of the Intra-Regional Trade Community Structures of the Indian Ocean Region

ISPRS International Journal of Geo-Information ◽

10.3390/ijgi10040214 ◽

2021 ◽

Vol 10 (4) ◽

pp. 214

Author(s):

Lihua Yuan ◽

Xiaoqiang Chen ◽

Changqing Song ◽

Danping Cao ◽

Hong Yi

Keyword(s):

Indian Ocean ◽

Explanatory Power ◽

Community Structures ◽

Indian Ocean Region ◽

Spatiotemporal Evolution ◽

Regional Trade ◽

Determinant Factors ◽

Ocean Region ◽

The Indian Ocean ◽

The Impact

The Indian Ocean Region (IOR) has become one of the main economic forces globally, and countries within the IOR have attempted to promote their intra-regional trade. This study investigates the spatiotemporal evolution of the community structures of the intra-regional trade and the impact of determinant factors on the formation of trade community structures of the IOR from 1996 to 2017 using the methods of social network analysis. Trade communities are groups of countries with measurably denser intra-trade ties but with extra-trade ties that are measurably sparser among different communities. The results show that the extent of trade integration and the trade community structures of the IOR changed from strengthening between 1996 and 2014 to weakening between 2015 and 2017. The largest explanatory power of the formation of the IOR trade community structures was the IOR countries’ economic size, indicating that market remained the strongest driver. The second-largest explanatory power was geographical proximity, suggesting that countries within the IOR engaged in intra-regional trade still tended to select geographically proximate trading partners. The third- and the fourth-largest were common civilization and regional organizational memberships, respectively. This indicates that sharing a common civilization and constructing intra-regional institutional arrangements (especially open trade policies) helped the countries within the IOR strengthen their trade communities.

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