Understanding Of Sea-level Changes Research Articles

Astronomical pacing of third-order sea-level sequences during the middle miocene in the northern south China sea

The Miocene Hanjiang Formation of the Pearl River Mouth Basin (PRMB) forms one of the most productive hydrocarbon reservoirs in China. Sparse biostratigraphic age control and limited dating hinder a thorough understanding of sea-level change and its sedimentary expression through this formation. To establish the relationship between third-order sea-level changes, their expression in the lithological record and astronomical forcing, a sequence stratigraphic and cyclostratigraphic analysis has been conducted through the Hanjiang Formation in the LF14 borehole. One second-order sequence and six third-order sequences are recognized based on gamma ray (GR) data, vertical lithofacies changes and sedimentary stacking patterns. Time series analysis of the GR data and subsequent interpretation allows recognition of approximately eighteen 405 kyr long eccentricity cycles. Based on this cyclostratigraphy, we constructed a ∼7.22-Myr floating astronomical time scale (ATS) for the Hanjiang Formation. We anchored this timescale to globally significant biostratigraphic events preserved in the basin to build an absolute ATS spanning 17.423 ± 0.4 to 10.221 ± 0.4 Ma. A prominent ∼1.2-Myr periodicity is identified in the amplitude modulation (AM) envelope curves of ∼41-kyr obliquity cycles preserved in the record. This ∼1.2-Myr periodicity shows good agreement with our sequence stratigraphic analysis and global eustatic curves. Our results suggest that ∼1.2-Myr obliquity AM was the main driver of third-order sea-level change and sequence development in the PRMB. Combined application of cyclostratigraphic and sequence stratigraphic analysis (utilizing INPEFA and wavelet transform methods) are demonstrated to be useful for understanding the drivers and subdivisions of third-order sequence evolution on a regional scale.

Understanding past climate variation and environmental change for the future of an iconic landscape – K'gari Fraser Island, Queensland, Australia

The unique combination of landscapes and processes that are present and operate on Fraser Island (K'gari) create a dynamic setting that is capable of recording past environmental events, climate variations and former landscapes. Likewise, its geographic position makes Fraser Island sensitive to those events and processes. Based on optically stimulated luminescence dating, the records archived within the world's largest sand island span a period that has the potential to exceed 750 ka and contain specific records that are of extremely high resolution over the past 40,000 years. This is due to the geographic position of Fraser Island, which lies in the coastal subtropical region of Queensland Australia. Fraser Island is exposed to the open ocean currents of the Coral Sea on the east coast and the waters of Hervey Bay on its western margin and is positioned to receive moisture from the Indo-Australian monsoon, southeast trade winds and experiences occasional tropical and ex-tropical cyclones. We review literature that presents the current level of understanding of sea level change, ecological variation and environmental change on Fraser Island. The previous works illustrate the importance of Fraser Island and may link processes, environments and climates on Fraser Island with global records.

Comparing tide gauge observations to regional patterns of sea-level change (1961–2003)

Abstract. Although the global mean sea-level budget for the 20th century can now be closed, the understanding of sea-level change on a regional scale is still limited. In this study we compare observations from tide gauges to regional patterns from various contributions to sea-level change to see how much of the regional measurements can be explained. Processes that are included are land ice mass changes and terrestrial storage changes with associated gravitational, rotational and deformational effects, steric/dynamic changes, atmospheric pressure loading and glacial isostatic adjustment (GIA). The study focuses on the mean linear trend of regional sea-level rise between 1961 and 2003. It is found that on a regional level the explained variance of the observed trend is 0.87 with a regression coefficient of 1.07. The observations and models overlap within the 1σ uncertainty range in all regions. The main processes explaining the variability in the observations appear to be the steric/dynamic component and the GIA. Local observations prove to be more difficult to explain because they show larger spatial variations, and therefore require more information on small-scale processes.

Sea Level Changes past Records and Future Expectations

The history and development of our understanding of sea level changes is reviewed. Sea level research is multi-fascetted and calls for integrated studies of a large number of parameters. Well established records indicate a post-LIA (1850–1950) sea level rise of 11 cm. During the same period of time, the Earth's rate of rotation experienced a slowing down (deceleration) equivalent to a sea level rise of about 10 cm. Sea level changes during the last 40–50 years are subjected to major controversies. The methodology applied and the views claimed by the IPCC are challenged. For the last 40–50 years strong observational facts indicate virtually stable sea level conditions. The Earth's rate of rotation records a mean acceleration from 1972 to 2012, contradicting all claims of a rapid global sea level rise, and instead suggests stable, to slightly falling, sea levels. Best estimates for future sea level changes up to the year 2100 are in the range of +5 cm ±15 cm.

Termination of the Last Glacial Maximum sea-level lowstand: The Sunda-Shelf data revisited

The sea-level history around the last glaciation is in the focus of recent, controversial debates. A profound understanding of sea-level changes during this time interval is, however, essential since sea level is a central parameter in the climate system as well as a major force on continental margin sedimentation. Here, we present a seismic record together with augmented data from the Sunda Shelf [Hanebuth, T.J.J., Stattegger, K., Saito, Y., 2002. The architecture of the central Sunda Shelf (SE Asia) recorded by shallow-seismic surveying. Geo-Marine Letters 22, 86–94.] and compare our results in a careful evaluation with the sparse existing data sets of global validity, i.e. the Bonaparte Gulf record [Yokoyama, Y., Lambeck, K., DeDeckker, P., Johnston, P., Fifield, L.K., 2000. Timing of the Last Glacial Maximum from observed sea-level minima. Nature 406, 713–716.; Yokoyama, Y., De Deckker, P., Lambeck, K., Johnston, P., Fifield, L.K., 2001. Sea-level at the Last Glacial Maximum: evidence from nortwestern Australia to constrain ice volumes for oxygen isotope stage 2. Paleogeography Paleoclimatology Paleoecology 165, 281–297.], the Barbados coral record [Fairbanks, R.G., 1989. A 17,000-year glacio-eustatic sea level record: influence of glacial melting dates on the Younger Dryas event and deep ocean circulation. Nature 342, 637–642.; Peltier, W.R., Fairbanks, R.G., 2006. Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record. Quaternary Science Reviews 25 (23–24), 3322–3337.] and the latest numerical model of continental deglaciation [Peltier, W.R., Fairbanks, R.G., 2006. Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record. Quaternary Science Reviews 25 (23–24), 3322–3337.]. Sea level seems to have been lower shortly prior to the conventional Last Glacial Maximum (LGM; 21–19 cal kyr BP). The time interval around this glacial lowstand is not covered by ages from the Sunda Shelf, but documented by an ancient barrier — tidal-flat system. These palaeo-coastal relict forms indicate such an early lowstand some 5 m deeper than sea level was during LGM times. The LGM sea level on the Sunda shelf is recalculated to − 123 ± 2 m modern water depth. This depth fits nicely with the lowstand data derived from Barbados and the Bonaparte Gulf. The recently assumed 19-kyr sea-level rise is supported by the Sunda and Bonaparte data sets combined, although it might have started already as early as at 19.6 cal kyr BP lasting for some 800 kyr with an amplitude of at least 10 m. This early pulse-like rise might have played a crucial role in the physical preservation of the high-glacial to early deglacial deposits on the Sunda Shelf. The modelled sea-level history is, thus, supported with respect to an initial high-glacial lowstand prior to the LGM, which might be in apparent contrast to observations from Bonaparte. Nevertheless, field data suggest a glacial sea-level evolution about 10 m deeper than the model. Also, the gradual rising trend from 26 to 16 cal kyr BP, as deduced from the model, can definitively not be approved by any field data. However, our knowledge is still unsatisfactory and an expansion of field data from suited areas is urgently needed.

Benefits to Studies of Global Sea Level Changes from Future Space Gravity Missions

Global sea level rise will present a major scientific, environmental and socio-economic challenge during the 21st century. This paper reviews the main oceanographic and geophysical processes which contribute to sea level change, with particular emphasis on the ability of space gravity missions to contribute to an enhancement of our understanding of the various processes, and ultimately to a better understanding of sea level change itself. Of special importance is the need to understand better the ocean circulation, and the contribution of ocean thermal expansion to sea level change.

Foreword [to Long‐Term Sea Level Changes

This special section contains a selection of papers presented at the AGU Chapman Conference on Long‐Term Sea Level held in Snowbird, Utah, April 17–20, 1989. The conference was convened by Dork Sahagian and Anthony Watts and was attended by a group of researchers active in a wide range of subjects dealing both with causes and expressions of sea level change. Sea level variations form one of those central topics in earth sciences that is beginning to bridge the gap between otherwise remote fields such as postglacial rebound dynamics, intraplate tectonics, sedimentary geology, and isotope analysis.The conference was the site of intensive debate, and the papers presented in this special section demonstrate the need for an integrated approach to make further advances in our understanding of sea level change. Integrated research on fundamental questions, including the relative roles of tectonics and eustasy and the issue of global synchroneity of sea level change, has actually only recently begun. It is our hope that the present section will stimulate much further research on these topics.