Experimental investigations of the spatial and temporal variability of temperature in the near-surface layer with weak wind blowing

Abstract. In most regions of the ocean, nitrate is depleted near surface by phytoplankton consumption and increases with depth, exhibiting a strong vertical gradient in the pycnocline (here referred to as the nitracline). The vertical supply of nutrients to the surface euphotic zone is influenced by the vertical gradient (slope) of the nitracline, and the vertical separation (depth) of the nitracline from the sunlit, nutrient-depleted surface layer. Hence it is important to understand the shape (slope and curvature) and depth of the oceanic nitracline. By using density coordinates to analyze nitrate profiles from autonomous (APEX-ISUS floats) and ship-based platforms (WOA09, HOT, BATS and CalCOFI), we are able to eliminate much of the spatial and temporal variability in the profiles and derive robust relationships between nitrate and density. This allows us to characterize the depth, slope, and curvature of the nitracline in different regions of the world's oceans. The analysis reveals distinguishing patterns in the nitracline between subtropical gyres, upwelling regions and subpolar gyres. We propose a one-dimensional, mechanistic model that relates the shape of the nitracline to the relative depths of the surface mixed layer and euphotic layer. Though heuristic, the model accounts for some of the seasonal patterns and regional differences in the nitrate–density relationships seen in the data.

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A new approach to model the spatial and temporal variability of recharge to karst aquifers

Hydrology and Earth System Sciences ◽

10.5194/hess-16-2219-2012 ◽

2012 ◽

Vol 16 (7) ◽

pp. 2219-2231 ◽

Cited By ~ 58

Author(s):

A. Hartmann ◽

J. Lange ◽

M. Weiler ◽

Y. Arbel ◽

N. Greenbaum

Keyword(s):

Time Series ◽

Spatial Variability ◽

Temporal Variability ◽

Model Performance ◽

Spatial And Temporal Variability ◽

Hydrological Models ◽

Near Surface ◽

New Approach ◽

Spatially Distributed ◽

Karst Systems

Abstract. In karst systems, near-surface dissolution of carbonate rock results in a high spatial and temporal variability of groundwater recharge. To adequately represent the dominating recharge processes in hydrological models is still a challenge, especially in data scarce regions. In this study, we developed a recharge model that is based on a conceptual model of the epikarst. It represents epikarst heterogeneity as a set of system property distributions to produce not only a single recharge time series, but a variety of time series representing the spatial recharge variability. We tested the new model with a unique set of spatially distributed flow and tracer observations in a karstic cave at Mt. Carmel, Israel. We transformed the spatial variability into statistical variables and apply an iterative calibration strategy in which more and more data was added to the calibration. Thereby, we could show that the model is only able to produce realistic results when the information about the spatial variability of the observations was included into the model calibration. We could also show that tracer information improves the model performance if data about the spatial variability is not included.

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