Improving Sea Level Reconstructions Using Non-Sea Level Measurements

We present a new method for reconstructing sea level involving cyclostationary empirical orthogonal functions (CSEOFs). While we show results from a CSEOF reconstruction using basis functions computed from satellite altimetry and subsequently fit to tide gauge data, our focus is on how other ocean observations such as sea surface temperature can be leveraged to create an improved reconstructed sea level data set spanning the time period from 1900 to present. Basis functions are computed using satellite measurements of sea surface temperature, and using a simple regression technique, these basis functions are transformed to represent a similar temporal evolution to corresponding satellite altimeter-derived sea level basis functions. The resulting sea level and sea surface temperature basis functions are fit to tide gauge data and historical sea surface temperature data, respectively, to produce a reconstructed sea level data set spanning the period from 1900 to present. We demonstrate the use of this reconstructed data set for climate monitoring, focusing primarily on climate signals in the Pacific Ocean. The CSEOF reconstruction technique can be used to create indices computed solely from sea level measurements for monitoring signals such as the eastern Pacific (EP) El Nio-Southern Oscillation (ENSO), Central Pacific (CP) ENSO, and Pacific Decadal Oscillation (PDO). The EP ENSO, CP ENSO, and PDO signals are all well represented in the CSEOF reconstruction relying solely on sea level measurements from 1950 to present; however, significant improvement can be made in reconstructing these signals during the first half of the twentieth century by including sea surface temperature measurements in the sea level reconstruction procedure

Cyclostationary Empirical Orthogonal Function Sea-Level Reconstruction

Since 1993, satellite altimetry has provided accurate measurements of sea surface height with near-global coverage. These measurements led to the first definitive estimates of global mean sea-level (GMSL) rise and have improved understanding of how sea levels are changing regionally at decadal time scales. These relatively short records, however, provide no information about the state of the ocean prior to 1993, and with the modern altimetry record spanning only 20 years, the lower frequency signals that are known to be present in the ocean are difficult or impossible to resolve. Tide gauges, on the other hand, have measured sea level over the last 200 years, with some records extending back to 1807. While providing longer records, the spatial resolution of tide gauge sampling is poor, making studies of the large-scale patterns of ocean variability and estimates of GMSL difficult. Combining the satellite altimetry with the tide gauges using a technique known as sea-level reconstruction results in a data set with the record length of the tide gauges and the near-global coverage of satellite altimetry. Cyclostationary empirical orthogonal functions (CSEOFs), derived from satellite altimetry, are combined with historical sea-level measurements from tide gauges to create the Reconstructed Sea Level data set spanning from 1950 to 2009. Previous sea-level reconstructions have utilized empirical orthogonal functions (EOFs) as basis functions, but by using CSEOFs and by addressing other aspects of the reconstruction procedure, an alternative sea-level reconstruction can be computed. The resulting reconstructed sea-level data set has weekly temporal resolution and half-degree spatial resolution

Reconstructing Sea Level Using Cyclostationary Empirical Orthogonal Functions

Cyclostationary empirical orthogonal functions, derived from satellite altimetry, are combined with historical sea level measurements from tide gauges to reconstruct sea level fields from 1950 through 2009. Previous sea level reconstructions have utilized empirical orthogonal functions as basis functions, but by using cyclostationary empirical orthogonal functions and by addressing other aspects of the reconstruction procedure, an alternative sea level reconstruction can be computed. The procedure introduced here is capable of capturing the annual cycle and El Nio-Southern Oscillation (ENSO) signals back to 1950, with correlations between the reconstructed ENSO signal and common ENSO indices found to be over 0.9. The regional trends computed from the new reconstruction show good agreement with the trends obtained from the satellite altimetry, but some discrepancies are seen when comparing with previous sea level reconstructions over longer time periods. The computed rate of global mean sea level rise from the reconstructed time series is 1.97 mm/yr from 1950 to 2009 and 3.22 mm/yr from 1993 to 2009

Separating Decadal Global Water Cycle Variability from Sea Level Rise

Under a warming climate, amplification of the water cycle and changes in precipitation patterns over land are expected to occur, subsequently impacting the terrestrial water balance. On global scales, such changes in terrestrial water storage (TWS) will be reflected in the water contained in the ocean and can manifest as global sea level variations. Naturally occurring climate-driven TWS variability can temporarily obscure the long-term trend in sea level rise, in addition to modulating the impacts of sea level rise through natural periodic undulation in regional and global sea level. The internal variability of the global water cycle, therefore, confounds both the detection and attribution of sea level rise. Here, we use a suite of observations to quantify and map the contribution of TWS variability to sea level variability on decadal timescales. In particular, we find that decadal sea level variability centered in the Pacific Ocean is closely tied to low frequency variability of TWS in key areas across the globe. The unambiguous identification and clean separation of this component of variability is the missing step in uncovering the anthropogenic trend in sea level and understanding the potential for low-frequency modulation of future TWS impacts including flooding and drought

Contribution of the Pacific Decadal Oscillation to Global Mean Sea Level Trends

Understanding and explaining the trend in global mean sea level (GMSL) have important implications for future projections of sea level rise. While measurements from satellite altimetry have provided accurate estimates of GMSL, the modern altimetry record has only now reached 20 years in length, making it difficult to assess the contribution of decadal to multidecadal climate signals to the global trend. Here, we use a sea level reconstruction to study the 20 year trends in sea level since 1950. In particular, we show that the Pacific Decadal Oscillation (PDO) contributes significantly to the 20 year trends in GMSL. We estimate the PDO contribution to the GMSL trend over the past 20 years to be approximately 0.49 ± 0.25 mm/year and find that removing the PDO contribution reduces the acceleration in GMSL estimated over the past 60 years. Key Points The PDO has contributed 0.49 mm/yr to the current altimetry GMSL trend The PDO has a large impact on regional and global sea level trends Reconstructions allow for the study of decadal-scale climate variability

The Effect of the El Nino-Southern Oscillation on U.S. Regional and Coastal Sea Level

Although much of the focus on future sea level rise concerns the long-term trend associated with anthropogenic warming, on shorter time scales, internal climate variability can contribute significantly to regional sea level. Such sea level variability should be taken into consideration when planning efforts to mitigate the effects of future sea level change. In this study, we quantify the contribution to regional sea level of the El Niño-Southern Oscillation (ENSO). Through cyclostationary empirical orthogonal function analysis (CSEOF) of the long reconstructed sea level data set and of a set of U.S. tide gauges, two global modes dominated by Pacific Ocean variability are identified and related to ENSO and, by extension, the Pacific Decadal Oscillation. By estimating the combined contribution of these two modes to regional sea level, we find that ENSO can contribute significantly on short time scales, with contributions of up to 20 cm along the west coast of the U.S. The CSEOF decomposition of the long tide gauge records around the U.S. highlights the influence of ENSO on the U.S. east coast. Tandem analyses of both the reconstructed and tide gauge records also examine the utility of the sea level reconstructions for near-coast studies

An Ongoing Shift in Pacific Ocean Sea Level

Based on the satellite altimeter data, sea level off the west coast of the United States has increased over the past 5 years, while sea level in the western tropical Pacific has declined. Understanding whether this is a short‐term shift or the beginning of a longer‐term change in sea level has important implications for coastal planning efforts in the coming decades. Here, we identify and quantify the recent shift in Pacific Ocean sea level, and also seek to describe the variability in a manner consistent with recent descriptions of El Nino‐Southern Oscillation (ENSO) and particularly the Pacific Decadal Oscillation (PDO). More specifically, we extract two dominant modes of sea level variability, one related to the biennial oscillation associated with ENSO and the other representative of lower‐frequency variability with a strong signal in the northern Pacific. We rely on cyclostationary empirical orthogonal function (CSEOF) analysis along with sea level reconstructions to describe these modes and provide historical context for the recent sea level changes observed in the Pacific. As a result, we find that a shift in sea level has occurred in the Pacific Ocean over the past few years that will likely persist in the coming years, leading to substantially higher sea level off the west coast of the United States and lower sea level in the western tropical Pacific. Sea level in the Pacific has undergone a shift in the past 5 years, with sea level in the eastern (western) Pacific rising (falling) Sea level variability in the Pacific Ocean has been separated into a biennial oscillation mode and a decadal mode This shift appears to result from a change of phase of a low‐frequency climate signal, that could continue on for the next several year

Immunoglobulin expression in the endoplasmic reticulum shapes the metabolic fitness of B lymphocytes

The major function of B lymphocytes is to sense antigens and to produce protective antibodies after activation. This function requires the expression of a B-cell antigen receptor (BCR), and evolutionary conserved mechanisms seem to exist that ensure that B cells without a BCR do not develop nor survive in the periphery. Here, we show that the loss of BCR expression on Burkitt lymphoma cells leads to decreased mitochondrial function and impaired metabolic flexibility. Strikingly, this phenotype does not result from the absence of a classical Syk-dependent BCR signal but rather from compromised ER expansion. We show that the reexpression of immunoglobulins (Ig) in the absence of the BCR signaling subunits Igα and Igβ rescues the observed metabolic defects. We demonstrate that immunoglobulin expression is needed to maintain ER homeostasis not only in lymphoma cells but also in resting B cells. Our study provides evidence that the expression of BCR components, which is sensed in the ER and shapes mitochondrial function, represents a novel mechanism of metabolic control in B cells