Short Citation:
Center for Operational Oceanographic Products and Services, 2021: Sea Levels Online: Sea Level Variations of the United States Derived from National Water Level Observation Network Stations, https://www.fisheries.noaa.gov/inport/item/37628.

Item Identification

Title: Sea Levels Online: Sea Level Variations of the United States Derived from National Water Level Observation Network Stations
Short Name: sl_trend
Status: In Work
Abstract:

Water level records are a combination of the fluctuations of the ocean and the vertical land motion at the location of the station. Monthly mean sea level (MSL) variations were analyzed for 128 stations of the National Ocean Service's (NOS) National Water Level Observation Network (NWLON) having between 30 and 146 years of data. The sea level variations determined are the linear trend, the average seasonal cycle, and the interannual variability at each station. Monthly data up to the end of 2006 were used in the calculation and all stations had data spanning a period of 30 years or more. Since the derived trends include the local vertical land motion, they are spatially variable. Calculated MSL trends range from 9.85 mm/yr for Grand Isle, LA to -16.68 mm/yr for Skagway AK, and are consistent with previous trends published by NOS. Available data from this project include time series plots for each station of the monthly MSL with the seasonal cycle removed, a 5-month average, and the linear trend with its 95% confidence interval which was obtained after accounting for the average seasonal cycle; the seasonal cycle; the Interannual variation of mean sea level for all data to 2006; and the Interannual variation from 1980 to the present (updated monthly). The location and timing of any major earthquakes near stations in tectonically-active areas are noted since an associated vertical offset or a change in MSL trend is possible.

Purpose:

The mission of the National Ocean Service, Center for Operational Oceanographic Products and Services is to provide the national infrastructure, and the scientific and technical expertise to monitor, assess, and distribute tide, current, water level, and other coastal oceanographic products and services necessary to support NOAA's mission.

Notes:

7

Keywords

Theme Keywords

Thesaurus Keyword
ISO 19115 Topic Category climatologyMeteorologyAtmosphere
ISO 19115 Topic Category geoscientificInformation
ISO 19115 Topic Category oceans
ISO 19115 Topic Category transportation
NGDA Portfolio Themes National Geospatial Data Asset
NGDA Portfolio Themes NGDA
NGDA Portfolio Themes Water Oceans and Coasts Theme
None average seasonal cycle
None coastal monitoring
None interannual variability
None long-term water level station
None Mean Sea Level
None Monthly MSL Variation
None MSL
None MSL change
None NWLON station
None oceans
None sea level fall
None sea level rise
None sea level trends
None tides and currents

Spatial Keywords

Thesaurus Keyword
None Coastal U.S. territories
None Coastal United States
None U.S. Exclusive Economic Zone

Physical Location

Organization: Center for Operational Oceanographic Products and Services
City: Silver Spring
State/Province: MD

Data Set Information

Data Set Scope Code: Data Set
Maintenance Frequency: As Needed
Data Presentation Form: raster digital data
Distribution Liability:

Monthly mean sea level (MSL) variations were analyzed for 128 stations of the National Ocean Service's (NOS) National Water Level Observation Network (NWLON) having between 30 and 146 years of data to obtain the linear trend, the average seasonal cycle, and the interannual variations. Recorded water levels are a combination of changes in the sea level and the vertical land motion at the location of the gauge. Therefore, the trends derived are relative MSL trends and can be considered valid only for a region near the gauge with uniform vertical land motion. Calculation of absolute MSL trends requires the accurate determination of vertical land motion at the gauges and was beyond the scope of this project.

Support Roles

Data Steward

CC ID: 393227
Date Effective From: 2016-08-23
Date Effective To:
Contact (Position): User Services Team
Email Address: tide.predictions@noaa.gov
Phone: 301-713-2815

Distributor

CC ID: 393229
Date Effective From: 2016-08-23
Date Effective To:
Contact (Position): User Services Team
Email Address: tide.predictions@noaa.gov
Phone: 301-713-2815

Metadata Contact

CC ID: 393230
Date Effective From: 2016-08-23
Date Effective To:
Contact (Position): User Services Team
Email Address: tide.predictions@noaa.gov
Phone: 301-713-2815

Point of Contact

CC ID: 393228
Date Effective From: 2016-08-23
Date Effective To:
Contact (Position): User Services Team
Email Address: tide.predictions@noaa.gov
Phone: 301-713-2815

Extents

Currentness Reference: Publication Date

Extent Group 1

Extent Group 1 / Geographic Area 1

CC ID: 393233
W° Bound: -180
E° Bound: 180
N° Bound: 61.24
S° Bound: -14.28

Extent Group 1 / Time Frame 1

CC ID: 393232
Time Frame Type: Continuing
Start: 1854

Spatial Information

Spatial Representation

Representations Used

Vector: Yes

Access Information

Security Class: Unclassified
Data Access Constraints:

None

Data Use Constraints:

None

Distribution Information

Distribution 1

CC ID: 393234
Download URL: https://idpgis.ncep.noaa.gov/arcgis/rest/services/NOS_Observations/CO_OPS_Products/MapServer
Distributor:
Description:

Other Documents

File Type: ArcGIS Map Services
Application Version: 10.2

Distribution 2

CC ID: 393235
Download URL: https://tidesandcurrents.noaa.gov/googleearth.html
Distributor:
Description:

Other Documents

Distribution 3

CC ID: 393236
Download URL: https://tidesandcurrents.noaa.gov/sltrends/sltrends.shtml
Distributor:
Description:

Other Documents

File Type: tabular and digital data

URLs

URL 1

CC ID: 393226
URL: https://tidesandcurrents.noaa.gov/
URL Type:
Online Resource

Activity Log

Activity Log 1

CC ID: 393262
Activity Date/Time: 2016-08-23
Description:

Date that the source FGDC record was last modified.

Activity Log 2

CC ID: 393261
Activity Date/Time: 2017-04-05
Description:

Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using 'fgdc_to_inport_xml.pl' script. Contact Tyler Christensen (NOS) for details.

Activity Log 3

CC ID: 583899
Activity Date/Time: 2017-09-13
Description:

Partial upload of Spatial Info section only.

Activity Log 4

CC ID: 598757
Activity Date/Time: 2017-11-01
Description:

Replaced entire Lineage section to populate new Source Contribution field.

Activity Log 5

CC ID: 716318
Activity Date/Time: 2018-02-08
Description:

Partial upload of Positional Accuracy fields only.

Data Quality

Accuracy:

The 95% confidence intervals of the MSL trends for all water level stations are listed in NOS CO-OPS Technical Report 36. The range of confidence intervals are inversely proportional to the length of the data series. The data time periods vary from a minimum of 30 years up to 146 years. The widest confidence intervals are for the stations with the shortest time periods of data.Since most of the U.S. east coast stations have been in operation for many years, the trends are well determined showing narrow confidence intervals. The stations south of The Battery generally have a greater MSL trend than stations north of The Battery. New Rochelle appears to have an anomalously low trend (0.54 mm/yr) based on 25 years of data (1957-1981) while Chesapeake Bay Bridge Tunnel appears to have an anomalously high trend (7.01 mm/yr) based on 25 years of data (1975-1999). However, comparable trends were found at nearby stations over the same 25-year periods. This indicates the danger in relying on only 25 years of data to determine a long-term MSL trend without considering the confidence interval.The U.S. west coast and Alaskan NOS stations have a greater variability of trends due to the variety of tectonic activity affecting vertical land motions. Often nearby stations have significantly different trends. Some of the newer west coast and Alaskan stations have wide confidence intervals due to shorter data sets. The most negative trend for all the stations is at Skagway where rapid vertical uplift due to local glacial rebounding is occurring. Four stations (San Francisco, Seward, Adak Island, and Unalaska) have separate trends determined for pre- and post- earthquake time periods. Although pre-earthquake trends for Adak Island and Unalaska are based on only 14 and 23 years of data, respectively, they are included for comparison with post-earthquake trends.There is somewhat less variability in the trends for the tropical Pacific, Bermuda, Gulf of Mexico, and Caribbean stations, except for a group of stations in Louisiana and part of Texas which show large positive trends. The stations in Louisiana and Texas are undergoing rapid land subsidence due to sediment loading and compaction of the Mississippi River delta and/or oil and gas extraction. In the Hawaiian Island, the station at Hilo has a larger MSL trend than the other Hawaiian stations. Hilo is on the volcanically active island of Hawaii, which is in the process of loading the Pacific lithospheric plate.

Vertical Positional Accuracy:

For most stations, the plotted values are relative to the 1983-2001 mean sea level datum.

Completeness Report:

Linear MSL trends were calculated for all NWLON stations with greater than 30 years of data. There are a wide range of error bars associated with the trends. Most of this variation can be attributed to the length of the data time series. There are two stations that are clear outliers, Guam and Chuuk. These stations have 52 and 49 years of data respectively, but their standard errors of 0.9 mm/yr are similar to those of stations with only 25-30 years of data. This greater uncertainty in trend is due to the large magnitude of the ENSO events in the western Pacific Ocean.In order to investigate whether MSL trends have been changing recently, the trend for the period 1950-2006 was calculated for the sixty NWLON stations with data spanning these years. When the trend from each station's entire data set is compared to the 1950-2006 trend, at only three stations (Eastport, Portland, and Boston) is there a statistically significant difference. At these three northern U.S. Atlantic stations, the recent trends are significantly lower than each station's overall trends. At none of the stations is the 1950-2006 trend significantly higher than the station's overall trend.In order to compare linear MSL trends between NWLON stations without dependence on the lengths of the time series, linear mean sea level trends were calculated for overlapping 50-year segments, for the sixteen oldest stations. The differences between stations are mostly due to differences in vertical land motion. The most significant departure from the long term trend was at San Francisco and may have been caused by a small offset and/or a change in trend related to the 1906 earthquake.

Conceptual Consistency:

NOS has collected water level data for a span of more than 30 years at 128 locations. Although there may be long data gaps at some of the locations, the existing data can provide good estimates of linear MSL trends since the vertical datums have been carefully maintained through periodic leveling to stable benchmarks with respect to the adjacent landmass.Data collection at some stations has been discontinued, but a long enough span of data exists to produce accurate linear MSL trends. These stations and their termination years are Chuuk (1995), Seavey Island (1986), Port Jefferson (1992), New Rochelle (1981), Portsmouth (1987), Miami Beach (1981), Eugene Island (1974), Padre Island (1994), Newport Beach (1993), Rincon Island (1990), and Guantanamo Bay (1971).The dates of major earthquakes in the vicinity of a NWLON station are marked on each graph with vertical lines. These earthquakes can result in slip along a tectonic plate boundary, immediately affecting the water levels at nearby NWLON stations with an offset and/or change in the MSL trend. The occurrence of all major earthquakes near a water level station are noted, even if there is no obvious coseismic offset in the record. Previous studies have shown that a change in MSL trend may not become evident until several decades after an earthquake (Cohen and Freymueller, 2001).It can be observed that, for a given length of data, the stations in the Pacific Ocean, the western Gulf of Mexico, and Bermuda have greater standard errors than stations in the Atlantic Ocean, eastern Mexico, and the Caribbean Sea. This is because ENSO events result in roughly twice the variability for the first group of stations compared to the second group of stations.

Lineage

Sources

Sea Level Variations of the United States 1854-2006

CC ID: 598758
Contact Name: National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Center for Operational Oceanographic Products and Services (CO-OPS)
Extent Type: Range
Extent Start Date/Time: 1854
Extent End Date/Time: 2006
Citation URL: http://tidesandcurrents.noaa.gov/publications/techrpt36doc.pdf
Source Contribution:

Documents study procedures and results. | Source Geospatial Form: document | Type of Source Media: document

Process Steps

Process Step 1

CC ID: 598759
Description:

The data examined in this study consist of monthly mean sea levels (MSL) for 128 NWLON stations in operation for a span of at least 30 years. Although there may be long data gaps at some of the locations, the existing data provide good estimates of linear MSL trends since the vertical datums have been maintained though periodic leveling to stable benchmarks with respect to the adjacent landmass. The monthly means are an average of hourly water level heights for a complete month of data. The sea level variations determined in this study were the linear secular trend, the average seasonal cycle, and the residual variability at each station. Recorded water levels are a combination of changes in the sea level and the vertical land motion at the location of the gauge. Therefore, the trends derived are relative MSL trends and can be considered valid only for the region near the gauge with uniform vertical land motion. Calculation of absolute MSL trends requires the accurate determination of vertical land motion at the gauges and is beyond the scope of this study.In order to investigate whether MSL trends have been changing recently, the trend for the period 1950-1999 was calculated for the sixty NWLON stations with data spanning these years. When the trend from each station's entire data set was compared to the 1950-1999 trend, at only three stations (Eastport, Portland, and Boston) was there a statistically significant difference. At these three northern U.S. Atlantic stations, the recent trends are significantly lower than each station's overall trends. At none of the stations was the 1950-1999 trend significantly higher than the station's overall trend. The differences observed between stations, during this time period, were mostly due to differences in vertical land motion.The possibility that there are other 50-year periods with MSL trends statistically different than the overall trend is examined for sixteen of the NWLON stations with the longest data sets. Six Atlantic stations (Portland, Boston, The Battery, Baltimore, Charleston, and Cedar Key) have periods centered on years between 1930-1955 with significantly higher trends and/or periods centered on years between 1965 and 1975 with significantly lower trends. Seattle has a period centered on 1925 with a significantly lower trend and a period centered on 1945 with a significantly higher trend. For San Francisco, trends for 50-year periods centered from 1890 to 1915 are significantly lower than both the overall trend and the trend since the 1906 San Francisco earthquake. For periods centered on 1895, 1900, and 1905, the trend is actually negative. This suggests that there may have been a small vertical offset and/or change in trend caused by the earthquake.

Catalog Details

Catalog Item ID: 37628
Metadata Record Created By: Tyler Christensen
Metadata Record Created: 2017-04-05 11:05+0000
Metadata Record Last Modified By: Brianna Key
Metadata Record Last Modified: 2020-12-08 21:49+0000
Metadata Record Published: 2020-12-08
Owner Org: CO-OPS
Metadata Publication Status: Published Externally
Do Not Publish?: N
Metadata Next Review Date: 2021-12-09